Underground of the Petrovaradin Fortress is the best adventurous tourist attraction in Novi Sad. It consists of 4 floors, with the depth of 20 kilometers, but so far researchers explored only 16km. It was built between 1768 and 1776. The military used these underground chambers, corridors, and galleries and they were originally built for the military purpose. Underground is particularly suited for it because the land is a natural insulator of radio waves, noise, sunlight, telephone signals.
This underground military system was built to be in parallel with the same overhead. Such construction prevented the Ottoman Empire from using their greatest tactical weapon – “night undermining the walls.” Also, the galleries are the great fortress defense system with the barricades and a series of tunnels and corridors with mine traps. Reconstruction of the military underground was in June 2009 and since then, they are open for visitors who usually come in organized groups within a very interesting tour with their tour guides.