Designed to provide the ultimate in security, military bases never come cheap. But on top of the eye-watering sums of money required to get them up and running, facilities for the armed forces can also be outrageously expensive to decommission.
Read on as we infiltrate 10 of the world's most jaw-dropping abandoned bases, revealing how much they cost to construct and, in some cases, shut down.
All dollar amounts in US dollars.
Spanning more than 13,000 acres, the Savanna Army Depot lies on the banks of the Mississippi River, not far from the city of Savanna in Illinois. The installation was built in 1917 as a testing ground for artillery. The total cost of construction was $585,000, which translates to around $15 million (£11.8m) in today's money.
By the 1920s, the facility was being used to manufacture, store, and test armaments, including chemical weapons such as mustard gas.
Savanna grew to become the biggest munitions storage base in America during World War II. The depot had a workforce of thousands in its heyday, but staff numbers dwindled as usage of the depot waned and dropped to 500 in the early 1990s. The end of the Cold War was the final nail in the coffin.
The depot was selected for closure in 1995 and eventually shut down in 2000. As you might imagine, toxic pollutants and unexploded ordnance litter the site, parts of which remain extremely dangerous.
In fact, the clean-up operation, which has been dragging on for years, has cost the US authorities well over $200 million (£157m) to date. The final bill is expected to sit at around $350 million (£275m), eclipsing the initial cost of the facility.
The good news is the core site, which is strictly out of bounds to the public, is now a haven for wildlife. The lack of human activity in the area has resulted in the ideal habitat for an impressive 47 plant and animal species that are threatened or endangered in the State of Illinois, including the ornate box turtle.
Set up by the US military in 2008, this forward operating base in eastern Afghanistan was used by Coalition troops as a strategic hub and location to train the Afghan National Security Forces and police.
Millions of dollars were spent building and expanding the facility, with the base turning into something of a money pit, swallowing up vast amounts of taxpayers' cash. The US military dropped $6 million (£4.7m) on security fencing alone, and splurged $12 million (£9.4m) on a 1.4 mile-long (2.3km) runway.
Given all the money ploughed into the base, it certainly wasn't lacking in amenities. FOB Shank had everything from a 50-store shopping mall to three restaurants and, surprisingly, four beauty salons.
But big changes came in 2014 when the majority of US troops withdrew from Afghanistan. The base was handed over to the Afghan police and has been largely unused ever since.
The crumbling base has been nicknamed “Zombieland” and likened to the TV show The Walking Dead by US soldiers, while the Afghan security forces refer to the dilapidated buildings as “houses for demons”.
Packs of wild dogs roam the landscape, adding to the post-apocalyptic feel. To this day, FOB Shank lies deserted and unmaintained.
Reminiscent of the Martian tripods in HG Wells' sci-fi classic War of the Worlds, the imposing Maunsell naval and army forts were erected in the Thames Estuary between 1942 and 1943 to defend London against Nazi air and sea attacks. The structures were named after their designer, Guy Maunsell.
Four naval and three army forts were built at a cost of £724,000, which works out at around £40 million ($51m) in today's money.
Equipped with searchlights and anti-aircraft guns, the forts made for a formidable defensive measure. By the end of World War II, they had destroyed a German E-boat and shot down 22 enemy aircraft and 30 flying V1 bombs.
However, the military swiftly abandoned the naval forts following the war. Today, only two remain: Knock John Fort, which was used in the late 1960s to broadcast pirate radio station Radio Essex, and Fort Roughs, aka the Independent Principality of Sealand.
Plans to redevelop the dilapidated and ramshackle facilities have been floated over the years, including a $127 million (£100m) project to transform one of the forts into a luxury hotel. However, no single plan has made it off the drawing board so far.
Chanute Air Force Base in Champaign County, Illinois was established during World War I as Chanute Field, a primary training school to instruct cadets in the rigours of flying warplanes. The installation was completed in 1917 at a cost of $1 million, well over $20 million (£16m) in today's money.
Two colossal hangars were built on the site in the late 1930s. The base was further expanded during World War II when accommodation for 15,000 personnel was built. A Women's Army Corps school was also set up during the conflict.
Following World War II, Chanute remained a crucially important training base. It prepped pilots for active combat in the Korean War and was the primary training centre for the LGM-30 Minuteman intercontinental ballistic missile during the 1960s.
As was the case with several other bases in our round-up, the end of the Cold War hastened Chanute's demise. The facility was deemed superfluous to the needs of the US military, which went on a downsizing spree during the early 1990s.
The base closed for good in December 1993. Since then parts of the site have been repurposed as housing, motels, a gym, and restaurants, but a significant proportion of the facility remains derelict and out of bounds.
These areas are heavily contaminated with toxins and the clean-up job is ongoing. To date, at least $200 million (£157m) has been spent and there's still some way to go until the entire site is made good. The US Air Force recently returned control of the base and its land to civilian hands. It's estimated that 480 acres of the site remain unused.
The gigantic Kaunas Fortress in south-central Lithuania was built over a period of 33 years from 1882 to 1915 to protect the Russian Empire, which controlled the area at that time, against German invasion. Upon its completion, the military base was the largest defensive structure in the country.
All in all, nine forts and nine batteries were constructed on the site. Fort IX, the largest of the structures, cost an estimated $7.6 million to build, more than $250 million (£196m) in today's money.
Kaunas Fortress had its first serious test during World War I when it was besieged by German forces. Despite relentless bombardment, the facility held out for an impressive 11 days, a testament to its robustness.
The history of the fortress took a darker turn during World War II when Kaunas was captured and occupied by Nazi troops. As many as 50,000 people were executed in the fortress, including 30,000 Holocaust victims.
After the war, the fortress was used by Soviet airborne troops until the late 1950s. In 1958, it was dedicated as a museum to memorialise the crimes perpetrated there and detail its history. A striking memorial standing 105 feet tall was unveiled at the site in 1984.
Fort IX, which was partly renovated in 2007, houses an exhibition of artefacts and welcomes hundreds of thousands of visitors a year. The rest of the site is little more than a ruin.
This top-secret missile base near Lake Plateliai in what is now Lithuania was built by a workforce of 10,000 men from 1960 to 1962. The mostly subterranean facility was far from economical to construct. In fact, the final bill was equivalent to the cost of building a small town, representing billions in today's money.
As you might imagine, security was exceedingly tight. The base was encircled by an electric fence capable of delivering a fatal shock of 1,700 volts.
Consisting of several deep shafts, several missile silos, and a maze of tunnels, the installation was large enough to house hundreds of personnel and could remain completely autonomous for up to 15 days. The silos contained numerous R-12 Dvina missiles fitted with nuclear warheads.
Thankfully, the thawing of Cold War tensions following the Cuban Missile Crisis meant the weapons were never deployed, even for testing purposes.
In the end, the outrageously expensive base was in operation for only 12 years. Maintenance of the site continued for a time but ceased in the early 1990s following the collapse of communism and break-up of the USSR.
The base deteriorated fast and became a magnet for trespassers. However, in 2012 some restoration work was carried out, and Plokštinė is now the home of the Cold War Museum, a popular tourist attraction.
Designated a fort in 1940 and closed in 1994, Fort Ord in coastal Monterey County, California sits on 28,000 acres of prime real estate. The area the fort encompasses is around the same size as San Francisco and is worth billions of dollars.
The facility dates from 1917, when it served as a manoeuvre area and field artillery target range. Fort Ord's expansion and designation as a fort cost $15 million, which comes in at around $300 million (£235m) in today's money.
The US Army's 7th Infantry Division was stationed at Fort Ord for much of its history. In World War II, German prisoners of war were imprisoned at the installation and tasked with constructing walls and bunkers.
After World War II, the fort was used as a training facility and became America's leading instructional installation during the Vietnam War. Soldiers jumped at the chance to be stationed there thanks to the fort's wonderful climate, oceanside location, and first-class amenities.
During the 1960s, the enormous base boasted a hospital, six schools, stores including a barbers and thrift shop, two movie theatres, a bowling alley, an 18-hole golf course, and an Olympic-sized swimming pool. However, the end of the Cold War rendered Fort Ord obsolete, and the facility eventually closed in 1994.
The decommissioning project and clean-up are estimated to have cost $332 million (£260m). Though many of the fort's military structures remain, much of the land has been sold off to private developers. Part of the site was awarded National Monument status in 2012.
Carved into a mountain, this covert naval base near Tromsø was built by the Norwegian Navy in the late 1960s. It cost an absolute fortune: the final bill came in at $494 million, around $4 billion (£3.1bn) in today's money.
No expense was spared on the base, which was equipped with the most advanced and sophisticated technology money could buy and featured 150,000 square feet (13,935 square metres) of buildings above ground and a plethora of tunnels and rooms beneath the mountain.
The Bond villain-esque facility was the primary supply and service base for NATO submarines operating in the Norwegian and Barents Seas. The subs navigated in and out of the installation via nifty canals.
But Olavsvern lost its key strategic importance following the fall of communism. The base was retired in 2002 and shut down in 2009 by the Norwegian government, which put it up for sale at a rock-bottom price.
The installation was eventually sold in 2011 to a consortium of Norwegian oil companies for just $5 million (£4m), a fraction of what it cost to construct. The former base was to have been used as a maintenance site for the oil industry.
Instead, much to the Norwegian government and NATO's chagrin, the base was rented by affiliates of the Kremlin-linked Russian energy giant Gazprom. It's now back in the hands of a Norwegian group and is in the process of hosting military units once again.
Željava Air Base was built by the Yugoslav armed forces between the late 1940s and early 1960s under a mountain at a secret location on what's now the border of Bosnia and Herzegovina and Croatia. One of Europe's largest military facilities, the cavernous installation served as a command centre and housed a missile early warning system.
Accessed by four entrances in the mountain, the underground part of the base was designed to be big enough to accommodate 1,000 personnel, launch jets from the entrances, and survive a direct hit from a 20-kiloton nuclear warhead.
The facility featured four reinforced nuclear blast doors capable of withstanding a nuclear bomb equivalent to the one that devastated Nagasaki at the end of World War II. Each of the doors weighed 100 tonnes intact.
The base's nerve centre, the star command hub, is pictured here. The intel-gathering and control facility is located at the locus of a network of subterranean tunnels that stretch over a staggering 2.2 miles (3km).
Above ground, the base was kitted out with five extra-long runways. Surveillance radars were placed on the top of the mountain, which was protected by surface-to-air missile interceptor systems and heavily guarded 24/7. The base is estimated to have cost $6 billion (£4.7bn) to build, a staggering $62 billion (£49bn) in today's money.
Despite the vast expense, the withdrawing Yugoslav People's Army destroyed much of the complex during the Yugoslav Wars in 1991 to prevent the opposing forces from using it for their own ends. The complex has remained abandoned ever since.
A bewildering waste of taxpayers' money, the Stanley R. Mickelsen Safeguard Complex in Nekoma, North Dakota was completed in April 1975 at a cost of well over $7 billion (£5.5bn) in today's money.
The futuristic complex, which was built beneath and around an eye-catching pyramid structure, provided launch and control for scores of short and longer-range anti-ballistic missiles.
Unbelievably, the multibillion-dollar state of the art facility was fully operational for just 24 hours. In October 1975 Congress deemed the base ineffective, pulled funding and voted to decommission the whole shebang, literally a day after it went from initial to full operating capacity.
The base was deactivated in February 1976 and pretty much abandoned by the authorities. In 2012, the US military put the complex up for sale in a bid to claw back some of the money invested in it.
The Stanley R. Mickelsen Safeguard Complex was snapped up by a religious group named the Spring Creek Hutterite Colony. The organisation paid $530,000 (£417k), a relatively meagre sum considering how much the base cost to construct.
Today, like many of the bases featured in our round-up, the Stanley R. Mickelsen Safeguard Complex stands as a monument to unbridled military overspending and pricey government policy U-turns.
Now discover the incredible underground megaprojects abandoned to time