Somewhere outside Sarajevo, Bosnia, looming over a small town called Visoko, sits the mysterious Visocica hill, which renegade researchers now claim to be a man-made structure: a pyramid estimated to be 235m high, one-third taller than the Great Pyramid of Giza in Egypt.

While experts say there is no scientific basis for his claims, 45-year-old Semir Osmanagic, an amateur Bosnia archeologist who has spent the last 15 years studying the pyramids of Latin America - is convinced that sitting underneath the hill is a giant step pyramid.

A large complex of ancient buildings—some which resemble the Mayan pyramids—has been discovered at the bottom of Fuxian Lake in southwest China’s Yunnan Province. The city also features rock roads, a round colosseum-like structure, and multi-level buildings reaching up to five stories with many small steps between the floors. Sonar surveys estimate the area of the city to cover nearly one square mile. Chinese television broadcasted video via an underwater autonomous vehicle which transmitted images of divers searching the site and unearthing artifacts including pottery and a piece of stone carved with floral patterns.