These columns are found in Varna, Bulgaria. They're hollowed out and filled with sand, almost perfectly round, and grouped together. And they're 100 percent natural formations. Sometimes even prehistory is in on the conspiracy to make us believe that we've discovered evidence of alien visitors.
These columns are no minor outcroppings. They can reach about ten meters tall, and stretch up to six meters wide. Some are hollowed out and filled with sand, while others are solid stone. They're called Pobiti Kamani, and they can stretch for miles.
To add to the mystery, no one is entirely sure how they formed. The most popular current theory aims to explain why they formed in Varna, rather than anywhere else. Methane seeps up in from the ground in several places around the area. Scientists believe that once, the area was covered with sea water. Methanotropic bacteria would live in a circle around a methane leak. They oxidized the methane and precipitated calcium carbonate. This calcium carbonate built up in the circles around each seep, and left these stone pillars behind.
Or the Floraxians used these as space-ship stands. You decide.