Pobiti Kamani

Pobiti Kamani, tubular concretions formed around "rising methane-bearing fluid plumes", is a desert-like rock phenomenon located on the north west Varna Province border in Bulgaria.

The stone pillars were first described by Russian archaeologist and historian Victor Teplyakov in 1829. In order to be preserved, Pobiti Kamani was designated a natural landmark in the late 1930s.There are a number of theories regarding the phenomenon's origin. The pioneering hypotheses can be divided roughly into two groups: suggesting an organic or abiotic origin.

Source: Wikipedia