Underneath the Plješivica mountains, the Željava airbase.

Deep beneath the hills of Plješivica, the Yugoslavian military dug like Tolkien’s dwarfs. They hollowed out the great mountain, creating mess-halls and assembly stations, aeroplane hangars and radar rooms, creating safety where none felt attainable during the cold war years after 1945. Željava airbase – codename ‘Objekat 505’, stretches over 3.5 kilometres underground, and it is into this dark place that I ventured.

From the outside the locale resembled a nature reserve. Looming mountains, a road overgrown and  bouncy with potholes, vegetation abundant, lush and heavy. The entrance to the cave gapped wide open and revealed a gallery blasted into the bedrock. The cavity was tattered and frayed with the living artefacts of a wild existence: dandelions, creepers, broadleaf bushes and deciduous trees, all scratching a living along the concrete boundary between runway and wilderness – between darkness and sunshine.

I went with a tour group of four other people – apparently someone had specially requested a trip to visit some of the key military sights important in the break up of Yugoslavia in 1991. But who that person was we never found out, I think the guide just liked it here, and I wasn’t about to argue with an adventure.

The cliff stood flat above me like some enormous forehead. I observed, the deep cracks that ran along its surface like the wrinkles on a perturbed mind. I wondered whether they’d crack and collapse onto our very heads as we passed beneath their scorn.  All around lay the rubble and refuse of this great subterranean airport, a dugout chasm of militaristic might. The entrance was blocked with a heap of concrete to stop people driving straight through to another country. What was once one was now two and  the five entrances opened between Bosnia and Croatia.

It’s dangerous. Dotted signs warned of mines still in the ground. The last victim reported online was in 2000. He was a mushroom picker, a Bosnian official, at least that’s how the story goes. I can’t help but think it would be the perfect place to fake an accident and carry out an assassination. Other dangers include the radiation from the disintegrated smoke alarms, and the chemical compound PCB which is lying around I gather. I don’t know where – just don’t lick the walls or take bits of rubble with you. Our guide jovially suggested that we shouldn’t worry about the mines. But the Bosnian Federation still use this ground to train its K9 units in finding explosives. I wouldn’t feel confident exploring alone and keeping my legs.

We looked up and down the concrete stretch – this was the first of two major runways, along with a three further, but smaller, taxi-ways. These were used as rapid reaction takeoff sites. I imagined the planes tottering out of the mountain before streaking into the skies.

Some estimates surmise that this entire place cost 6$ billion to make i.e. the most expensive European military instalment in history. It was rumoured to have acted a little like NORAD in Colorado, as an advanced warning base in case of nuclear war. Built from 1958 to around 1965, it was equipped with radar, but no nukes. It, however, was a secretive affair.

Some guy on a bike turned up and after a quick chat with our guide, accompanied us inside – I imagined he felt a little bit safer with a crowd. A wrong turn could take you to Bosnia and land you facing  the border police and a fine. But to my mind, this might be the least of your worries. I suspected smuggling by unsavoury characters. Regardless, you should always let officials know before you go nosing around. At Izačić (the border) we had already informed them of our intentions. On the way there, we drove past a landscape littered with burnt out buildings, pocked with bullets and empty of inhabitants. People not having the will nor the money to move back.

To this day, each former Yugoslavian country has committed to not having a military based within 15km of their border, so this ruin will last forever and it grows more unstable every year. The war in Croatia was slightly outside my time, coinciding with the fall of the Iron Curtain in 1991. I knew of it, but not much about it. I trace outlines on the map; trace the old borders of Yugoslavia, The USSR, find Kosovo, find East Germany and Czechoslovakia. Follow these old borders that still fall well within living memory. I considered the echos that touched decades of time, all fluttering out of that epicentre that was the Second World War – the second apocalypse – because we hadn’t learnt enough lessons with the first.

Inside, the silence was total, as was the dark. Our guide handed out some torches which needed a bit of shaking to stay awake. And even then he didn’t quite have enough, but I wasn’t bothered. I needed two hands for my camera.

The tunnels were all aeroplane sized. I pictured the shadowy hush their wingspans above me might have created. Then I thought about the soldiers and saw that stereotypical image – the same one used in films about the Napoleon war to those on Iraq – of men sitting around on crates, smoking and playing cards. Except in this picture they were called things like Ivan or Radič.

I read later online, that the mess hall could cater for up to 1000 men for 30 days should the mountain be hermetically sealed i.e. should it be forced to withstand a 20 kiloton nuclear warhead (the same size as the one that hit Nagasaki) which it was made to do. The place had an underground aquifer, and fuel was delivered via underground pipes from the nearby village of Bihać. It was a fortress.

We walked out of the second entrance past where one of the blast doors had been C4’d out of existence. Eyewitnesses say that the cavern smoked for the next 6 months – like the last cold breaths of a dragon. But I bet this place must have felt safe in its heyday. Wearing a stiff starched uniform, hunkering down under the protective hunches of Plješivica – safe in the belly of the beast amongst the two full fighter squadrons of MiG 21 jets. Nowadays though, I wouldn’t go too deep; the structural integrity of the base has been severely compromised by the bombs.

Outside stood an aeroplane – a Douglas C-47 shipped over when Yugoslavia still had good relations with the Americans. I hauled myself into the carcass of the plane. My fingers flicked all the switches still attached to the cockpit; moved the levers up and down. Still slightly afraid that the burned-out wreckage around me would shudder into life and take me away.