"The latests measurements show that the Martel Hall measures 2.55 million cubic metres, whereas until now it was believed that the hall was 2.2 million cubic metres," Rosana Cerkvenik of the Škocjan Cave natural park told the press earlier this week.

The hall is 314 metres long, 143 metres wide and measures 158 at its highest point, she said. The new measurements, acquired with laser scanners, make the chamber the second biggest in Europe and 11th biggest in the world.

The caves became a tourist destination in 1819, when an official log of visitors was started. One of the most significant names entered in the log is that of Stephanie, the crown princess of Austria.

The first path through the caves was built in 1823 by the local Matej Tominc, who is considered the pioneer of tourism of Škocjan Caves, which have so far been seen by about four million visitors.

The 200th anniversary has been marked by a number of events, while the main ceremony was held on Saturday, with President Borut Pahor delivering the keynote.