Mysterious medieval mazes, creepy catacombs, covert Cold War-era subterranean cities, war-time defence tunnels and underground passages used to smuggle goods, all kinds of secret spaces lurk below benign looking towns and cities.

Click through the gallery to see what lies beneath some of the world’s charming towns and small cities...

Perched high on a volcanic outcrop above green fields and vineyards, Orvieto is a postcard-perfect Umbrian hilltop town. The medieval centre hosts a grand Duomo, palazzos, monasteries, churches and myriad food and wine shops selling the region's revered wines. Dig a little deeper though and you’ll find that the tufa stone below its cobbled streets is riddled with man-made caves, tunnels, wells, quarries, kilns, cisterns and cellars – a world that originally dates back to the 9th century BC when the Etruscans dug tunnels to defend themselves from the Romans.

You can explore many of the city’s subterranean structures via guided tour (visiting the sites solo is not possible). Key features include a medieval olive oil mill with press and dovecotes, the maze-like tunnels of Labirinto di Adriano and the wells of Pozzo di San Patrizio and Pozzo della Cava. The latter is a 6th-century hand-dug Etruscan well surrounded by several chambers, including a medieval workshop and cellars. It's now the setting for an annual nativity display.

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The small rocky outcrop of Gibraltar, a British Overseas Territory protruding from Spain's southern coast, is best known today for Barbary macaques, British pubs and sunshine. But its most fascinating attraction lies out of sight: an intricate labyrinth of rock-cut tunnels that criss-cross through the limestone, carved across two centuries by the British army to protect the peninsula from sieges. First excavated during the Great Siege of Gibraltar between 1779 and 1783, the passages and vaults were extended significantly by the Royal Engineers and the Canadian Army just before the Second World War.

All in all, a 34-mile (55km) tunnel network was chiselled deep inside the rock, and it was used as a base for General Eisenhower to command the North African landings in the Second World War. It was large enough to accommodate a 16,000-strong garrison and store enough supplies to last them 16 months. Tourists can visit both the original Great Siege Tunnels and the Second World War Tunnels on guided tours. The latter includes an underground telephone exchange, a set of generators, a water distillation plant, a hospital, a bakery and a vehicle maintenance workshop. 

Comely Corsham sits on the edge of the Cotswolds, just outside Bath and surrounded by the pretty Wiltshire countryside. The small town is brimming with handsome period buildings thanks to a prosperous past when it was a centre for wool and stone. Many of the Georgian houses and cottages feature the local golden Bath stone (which was quarried here), as does the town's sprawling manor house Corsham Court. Home to the Methuen family since 1745, the palatial private estate is open to the public. 

You would never know from the picturesque spires and well-kept lawns that just 100 feet (30m) below the town lies a sprawling Cold War-era city, known as the Burlington Bunker. The Ministry of Defence commissioned the 35-acre underground complex to be built beneath Corsham in the late 1950s, and in the advent of a nuclear war it would have been the UK government's war headquarters. It could hold thousands of people and contained 60 miles (97km) of roads, while a secret railway branching off the London-to-Bristol line would have been used to save the royal family. The site was top secret until it was decommissioned in 2004 and is not open to the public.

With its age-old fortresses, watchtowers, Moorish streets and Roman remains, this attractive Spanish port has history around every corner. The city’s roots go far deeper though, as it was founded by Phoenician traders in 1100 BC and is one of the oldest continuously-inhabited cities in Europe. You can see remains of the original colony, known as Gadir, under the Teatro del Titere at the fascinating Gadir archaeological site.

Cadiz is latticed with ancient underground passages, caves and catacombs too, collectively thought to total around 37 miles (60km) below the city's bustling streets. These include galleries excavated under the Roman theatre (pictured) and Roman-era sewers, plus the eerie and only-recently-uncovered catacombs of Beaterio de Cadiz, a burial place for nuns from a 17th-century convent. The clandestine chambers were also used as hiding places during the Spanish Civil War and Spanish Inquisition. You can visit the complex on a guided tour.

Arras is a gem of a small city in northern France with large Baroque-style squares, an ornate town hall, belfry and a majestic star-shaped citadel (the belfry and citadel are both UNESCO World Heritage Sites). Beneath the streets of its historic quarter lie a series of galleries known as the Boves of Arras. These former chalk quarries were dug out 40 feet (12m) below the ground from the 9th century onwards to construct the city’s religious buildings and were later used as storage cellars by local merchants. However, they went on to play a much more important role in the city's story...

Located just a few miles from the Western Front, Arras and its secret tunnels were central to the Allies’ success in the famous Battle of Arras, which began on 9 April 1917 during the First World War. A workforce of New Zealand servicemen dug 12 miles (20km) of extra tunnels to link up with the original Boves, which sheltered 24,000 soldiers and enabled the Allies to move undetected to the enemy front line. One of the quarries, the Carriere Wellington, was restored and is now a museum and memorial. During the Second World War, civilians took shelter here during aerial bombardments. You can enter the Boves from the marketplace on the Place des Heros.

Once known as 'the Richest Hill on Earth' due to the vast quantities of gold, silver and copper unearthed here since mining began in the 1800s, the ground beneath Butte is riddled with mine shafts and long-abandoned pits. An astonishing 10,000 miles (16,093km) of tunnels were dug here in total, and locals often discover new openings to mine shafts in their gardens each spring when the snow melts. Away from the town's mining heritage, the historic district yields some intriguing underground spaces too...

Lying beneath the sidewalks of Main Street and under the historic Rookwood Hotel are chambers where a barber, shoe shop, jail and hidden bar from the Prohibition days once operated. Local lore holds that the above-ground town became so crowded at the turn of the century – its population hit 100,000 in 1917 with over 150 operational mines – that people began opening businesses underground. You can visit Butte’s hidden mini-city on a guided tour that takes in the Rookwood Speakeasy (pictured) and the Old City Jail. You can also head 100 feet (30m) down into the Orphan Girl Mine at the World Museum of Mining.

With its gorgeous Grote Markt square, grand city hall, gabled guild houses and art-filled Flemish museums, Antwerp is a fantastic city to explore. But few visitors look beyond its obvious charms to discover its endlessly fascinating underground world. Known as the Ruien, a medieval tangle of former sewers, vaults and canals lies underneath the streets and is now easily accessible to those in the know.

Like Bruges and Amsterdam, canals flowed through the port city’s streets in the 13th century providing both transport and defence, but they were largely covered for sanitary reasons and to make room for the construction of the enormous Sint-Carolus Borromeus church by the Jesuits in the 17th century. In 2005 the Ruien was repurposed as an unlikely tourist attraction, and visitors can now explore the underground network on walking tours. Better still, combine your ticket with a visit to the Jesuit church, before descending its cellar stairs and exiting through a secret corridor directly into this watery subterranean system. 

The rock fortress city of Valletta might be tiny, but its history is rich and battle-scarred. Underground passages were key to its construction when the Knights Hospitaller of Malta set about building the fortress after the Great Siege of 1565. The ambitious structure included underground water cisterns and tunnels for drainage along with passages designed for ventilation. Subterranean chambers were also built for grain storage, along with covert escape routes in case a siege went poorly. The city's capacity to conceal troops again came into play when Malta suffered aerial bombardments in the Second World War.

With its strategic position between Europe and North Africa, Malta played a crucial role during the war. You can find out more at the Lascaris War Rooms, a series of underground tunnels below the Upper Barrakka Gardens that were built in 1940. They were used as a top-secret military base and as Eisenhower’s command centre during the invasion of Sicily in 1943.

Another centuries-old fortified city sitting above an intriguing network of tunnels is the Estonian capital, Tallinn. Thought to date back to the 17th century, when the city was in the Swedish empire and under attack from Russia, the tunnels were built along Tallinn's earthwork fortifications on Toompea Hill. These covert passageways, now known as the Bastions, were used to hide the movement of forces and weaponry from the enemy as well as to spy on them.

These hidden passageways were also used as bomb shelters during the Second World War and were later repurposed by the Soviets as nuclear hideouts. Though they were off-limits for a long time, the tunnels are now visitable via the Kiek in de Kok Fortifications Museum, which is home to four of the old town's medieval defence towers as well as the Carved Stone Museum, located in the Inger Bastion tunnel. The tunnel (pictured) is hung with a display of decorative fragments that once adorned Tallinn's historic buildings. It tells the story of the city's renowned stone-carvers.

A handsome historic town on the banks of the Duero River in the province of Burgos, Aranda de Duero is a delightful place for a wander with its ancient laneways and impressive cathedral. The town became prosperous in the 15th century under the reign of Henry IV of Castile, with wine at the heart of its economy. Wine is still a big draw today, and Aranda de Duero is the capital of the Ribera del Duero wine region.

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The winemaking tradition runs deep – literally. Above ground, shops sell award-winning tempranillo, while below you'll find a series of ancient bodegas (underground wine cellars). Aranda de Duero has some five miles (7km) of subterranean cellars beneath its historic centre, which date from the 13th to 18th centuries. They were dug out by winemakers as storage spaces, and, though many have long been shut off, wineries like Bodega Historica Don Carlos have now opened their cellars as atmospheric venues for tastings. 

A quintessential fortified Tuscan city, Siena is packed with medieval treasures and steeped in age-old traditions. From its world-renowned Duomo and shell-shaped Piazza del Campo (pictured) to its 17 distinct 'contrade' (districts) and twice-yearly bareback horse race, Siena is endlessly intriguing. As with many ancient cities, though, it has a layered history, and below street level there lie plenty of secret spaces...

Underneath the old city’s towering palaces, busy piazzas and narrow lanes lies a system of tunnels known as the 'bottini'. Built around the 12th century, the underground aqueducts were used to bring water into the hilltop city to feed its fountains, cisterns and wells. The arched 13th-century Fontebranda near the Basilica of San Domenico is the city’s oldest fountain, which the bottini faithfully supplied. If you recognise the tunnels, that might be because they starred in a high-octane chase sequence in Bond movie Quantum of Solace. 

The small southern Italian city of Matera tumbles playfully down a limestone plateau. Underneath its narrow streets and cobbled courtyards lies an intricate and extensive warren of caves. The 'sassi', which means 'stones', are naturally-occurring caverns that once housed more than 1,000 houses, workshops, monasteries and hermitages. There is evidence the caves have been occupied since the Palaeolithic period, but by the 1950s the dwellings were overcrowded and home to impoverished families and their animals with no running water or electricity. The sassi were controversially cleared by the government, its residents rehoused.

In 1993 the vast complex, made up of districts Sasso Barisano and Sasso Caveoso, as well as Matera's remarkable rock-cut churches were inscribed as a World Heritage Site by UNESCO, which calls it 'the most outstanding, intact example of a troglodyte settlement in the Mediterranean region'. Some are now home to restaurants, bars, boutique hotels and stores. The intriguing site has also starred in numerous movies, including 2021 Bond film No Time to Die.

Humans have inhabited some strange places down the centuries, and Cappadocia in Turkey is testament to our capacity to thrive in the most hostile environments. The region is famous for its rock houses which were hewn straight out of the landscape, but sprawling underground settlements exist there too. On the surface Derinkuyu, which lies around 25 miles (40km) from Goreme, is home to a few normal houses, a handful of cafes and shops, and an abandoned Greek church (pictured). But what draws visitors is what lies beneath the dusty streets: the largest subterranean city in the already-extraordinary region.

The vast underground settlement was apparently rediscovered in the 1960s by a local, who stumbled upon a maze of narrow tunnels and dwellings behind a wall in his home while renovating. No one knows exactly how far back the caves go, but the network was heavily expanded during the Byzantine era (specifically during the Arab-Byzantine war of the 7th-11th centuries), where it was used both as a storage space and a defensive system to hide from foreign invaders. With an incredible 18 levels of tunnels, Derinkuyu could shelter 20,000 people and enough livestock to feed them for months.

Founded in 1882, the historic railroad city of Moose Jaw in southern Saskatchewan attracts a steady trickle of tourists with its petite downtown full of heritage buildings and its Mac the Moose statue (officially the world’s largest moose). But its best attraction lies below: secret tunnels allegedly used for rum-running in the US and Canada's Prohibition era when bootlegging, gambling and prostitution thrived in the small city.

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No one is quite certain why they were constructed, but you can delve into the city’s shady past at the Tunnels of Moose Jaw. The popular attraction offers guided 'theatrical tours' that give dramatised accounts of how the tunnels were used. The Chicago Connection tour brings to life the bootlegging era and Moose Jaw’s connection to Al Capone (local lore has it that the notorious gangster may have hidden out here). Alternatively, the Passage To Fortune tour details the hardships faced by early Chinese immigrants working on the railroad, and posits a theory that the tunnels may have been constructed after Chinese immigrants were pushed to live underground to escape hostility and racism.

Czechia’s handsome second city and the capital of South Moravia, Brno is a bustling place with a lively bar and cafe scene, dotted with historic monuments like the imposing Spilberk Castle. It's also home to a number of intriguing underground spaces, and beneath the town’s open-air Cabbage Market lies a series of medieval passages and cellars once used to store food, as well as a pillory and an alchemist’s laboratory.

Another underground area was discovered in 2001, under the floor of Brno’s 13th-century Church of St James. The second largest ossuary (a chamber where human bones are placed) in Europe after the catacombs of Paris, the three-chamber crypt was most likely built in the 17th century and is estimated to contain the remains of over 50,000 people. Analysis suggests it was a burial place for victims of plague and cholera during the Thirty Years' War. The atmospheric tunnels are open for tours.

On the surface, scenic Sweetwater in Tennessee might make you feel like you’ve travelled back in time. This small American city’s historic shopping district is home to renovated buildings that capture the essence of the town’s 1875 origins. It’s a place to discover rare antiquities, beautiful furniture and original works of art. What lies beneath Sweetwater, however, proves once and for all that you should never judge a book by its cover.

Hidden 140 feet (43m) below Sweetwater, you’ll find The Lost Sea – an enormous cavern that’s home to the largest underground lake in the United States. The visible portion of the lake, discovered by a 13-year-old-boy named Ben Sands in 1905, measures 880 feet (268m) long by 220 feet (67m) wide. Despite being known about for over a century, cave divers continue to map its murky depths to this day. Glass-bottomed boats powered by electric motors help visitors to explore the water’s surface here. Fishing might not be permitted but you can still keep an eye out for the largest rainbow trout in North America while you’re down here.

Nestled in Virginia’s Shenandoah Valley, you’ll find the small yet incredibly picturesque town of Luray. What this place, with its population just under 5,000, lacks in size, it more than makes up for with its wide and varied offering of attractions. If architecture from the 19th century is what you’re after, for example, head to the Luray Valley Museum. Petrolheads, meanwhile, can make for The Car and Carriage Caravan Museum and its excellent collection of vintage vehicles. There’s also a beach and nature trail to enjoy at nearby Lake Arrowhead.

In this corner of Virginia, it's in the Luray Caverns where things get really interesting. The largest cavern in the eastern United States is like few places on Earth, transporting visitors to what feels like another planet as soon as they set foot inside. This huge underground space – with its 10-storey-high ceilings – houses an incredible lake and the world's largest musical instrument. The Great Stalacpipe Organ, which covers 3.5 acres of the cavern, makes music by gently tapping stalactites. 

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