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.