The Mysterious Underground of Croatia

Due to its excellent geostrategic position, Croatia was a conflict zone several times, and due to the coast on one side and the distance from the state borders of the countries, which Croatia was part of until its independence, there are many military facilities in Croatia, including an underground one, which are already becoming tourist attractions.

In this travelogue, we’ll visit three areas where megalomaniac underground objects are located, which were and are still spoken of in superlatives. We’ll visit the Velebit underground, more precisely the bunker for the leadership of the Socialist Federal Republic of Yugoslavia, including the Supreme Commander Josip Broz Tito, from the 1950s, which is now a tourist attraction within the Paklenica National Park. Another facility that we’ll visit in this travelogue is the largest underground airport in Europe, located in Željava, on the border between Croatia and Bosnia and Herzegovina not far from the Plitvice Lakes. The underground airport is currently accessible, but not regulated as a tourist attraction, so certain precautions should be taken. The third underground “delicacy” is located in Pula. It’s a system of tunnels under the city that served as a shelter and much more.

What do we find in Velebit?

That’s exactly what I meant – not on Velebit, but actually in Velebit, as we’ll go inside a hill in which a huge underground building was built in strict secrecy, which served as a shelter for the narrow leadership of the Socialist Federal Republic of Yugoslavia, including the President and Supreme Commander Marshal Tito. The project dates back to the 1950s and was built as a shelter for the state leadership in the event of Soviet aggression. The bunker was so well built that it could withstand an attack with nuclear weapons. Most fascinating is its functionality, as the bunker was self-sufficient for an extended period of time, and the vertical ventilation shaft reached to the top of the hill, thus providing an independent source of clean air. The bunker was built between 1950 and 1953, but, after Stalin's death in 1953, it lost its basic purpose, as the danger of a Soviet attack also diminished.

With the beginnings of tourism in the seaside town of Starigrad - Paklenica, Paklenica has also become an interesting tourist attraction. It was declared a protected forest area as early as 1949 and a national park in 1997. This hidden underground facility was located in the immediate vicinity of the hiking trail, but even the locals didn’t know about it until the Croatian Homeland War, when the Croatian army discovered and began to use it as a warehouse.

Today, the facility can be visited during a visit to the Paklenica National Park, and the bunker has a conference hall, a buffet, an exhibition space and even a climbing wall. In the summer months, a visit to the bunker isn’t only an experience but also a refreshment, as the temperature inside is significantly lower than the one in the surroundings.

And if, in the case of the Underground City of Paklenica, we’re talking about a well-organised tourist facility, the Željava facility, Object 505 or Klek 505 is something completely different.

The mysterious "KLEK 505" object

Klek 505 is located in the Plješevica Mountain and is the largest known underground military airport in Europe. The idea dates back to the late 1940s, and construction began in 1956 and lasted until 1968. The size of the building itself is evidenced by the cost, which was between six and eight billion US dollars, which today, given the revaluation, meant 40 billion euros. The underground military base and military airport was a self-sufficient facility that, along with personnel, would have survived an explosion of a 20-kiloton nuclear bomb directly on a mountain slope or in front of the entrance to the facility.

In three and a half kilometres of tunnels, there was enough space for at least two air squadrons, among other things, and there were 58 MIG-21 aircraft in the facility itself. The facility is located entirely in the territory of the Republic of Croatia, while the runways are partly located in the area of today's Bosnia and Herzegovina. The location itself was strategically chosen, as it was just far enough away from the Hungarian border, from where a possible attack by the Soviet Union was expected, and equally far enough from the Italian border and coast, from where a possible attack by the US was envisaged. The natural conditions were additionally favourable, as the planes were in the radar shadow of the Plješevica Mountain when they took off, and so the radars would detect them only when they developed sufficient speed and reached an altitude at which they could effectively intercept enemy aircraft.

The air base itself (and especially its entrance) was designed for MIG-21 aircraft, as the entrance door was made in the silhouette of this aircraft and therefore wasn’t able to host the newer MIG-29 fighters. The silhouette of the building was one of the technical limitations in the project of the Yugoslav supersonic military aircraft, which, however, was stalled in the final phase due to the disintegration of Yugoslavia.

Many secrets were connected with the object, which isn’t surprising, as supersonic fighter jets took off from the mountain and disappeared into it. During the Croatian Homeland War, the then Yugoslav People's Army decided to evacuate the military facility, destroying everything that couldn’t be taken away, and blowing up all vital parts of the underground facility including runways.

Taking photos next to an abandoned Douglas C-47 Dakota aircraft

The facility is located not far from the Plitvice Lakes in Željava, where an abandoned Douglas C-47 "Dakota" military aircraft from World War II, which was used by the Yugoslav Army after the war, awaits you at the entrance to the former military area. Related to this plane is one very special incident from 2017, when the police caught two Belgian citizens during the theft of the plane. At the time of writing, it was possible to enter the area, but I advise the utmost caution when visiting, as the facility is located on the border with Bosnia and Herzegovina, and there’s danger of inadvertently crossing the state border illegally. In addition, it should be noted that the airport was mined during the last war and that it hasn’t been completely demined to date. When visiting, I therefore warmly recommend that you don’t leave the cleaned-up paths, but in any case, I recommend visiting at least part of the tunnel that’s been cleaned up and a panoramic ride along the longest preserved runway.

To explore the Paklenica National Park and this part of Dalmatia in general, book a youth hostel in Zadar, where you can spend quality and safe nights for less money.

If the first two underground military facilities are from the times of the former Yugoslavia, the underground of Pula has a slightly longer history.

Underground labyrinths of Pula

Pula has always been an important military port and so we can find megalomaniac military facilities in the city, dating from the period of the Austro-Hungarian monarchy, Italy and Yugoslavia, although due to its geostrategic location it was an important city in Roman times from which the most famous building in Pula originates – the Pula Arena, which still serves entertainment today, only the gladiators were replaced by musicians and film actors either live or on the big screen.

Pula was the main military port of the Austro-Hungarian monarchy and as such it was also one of the major targets for enemies. Therefore, in addition to protective facilities at sea, from anti-submarine nets to the "breakwater", a kilometre wall in the sea that protected the port of Pula from ships and submarines, a system of underground shelters and warehouses was also built. But given that the threat of airstrikes in World War I was almost nil, the shelters were also quite modest. Only three per cent of the Pula underground was to be built before World War I, a further ten per cent until the beginning of World War II, and the rest was built during World War II. There was enough space for 50,000 people in the shelters in the Pula underground, which is only a little less than Pula’s population today. After World War II, certain shelters were fortified to withstand a possible nuclear attack, and some new ones were built. The system of tunnels, shelters and warehouses is located below the hills of Kaštel, Monte Zaro and Monte Ghiro, three of the seven hills on which ancient Pula grew, and these seven hills are one of the reasons why the Romans decided to place the city right here.

The tour of the underground Pula was just before the opening at the time of writing, so it’s probably already open at the time you’re reading this. Part of the underground tunnels under the Kaštel hill will be open to visitors, where there’s also a city museum, which will be connected to the elevator by tunnels. There will also be an exhibition space in the labyrinth of underground corridors, which was in the last phase of preparation during my visit, so you’ll be able to escape the afternoon heat in a “cultural way”.

Before leaving, don't forget to book an overnight stay in the Youth Hostel Pula, where you can refresh yourselves on the beach, which is used mainly exclusively by the guests of the hostel.

In the end, I just wish you a plentiful cultural, sports and entertainment experience during your exploration of Croatia, both below the surface and, above all, of course on the surface.