While we're (justifiably) slapping each other on the backs because we landed a space probe on a rock 500 million kilometers away, it's worth keeping in mind that there's a ruined fortress on a six-hectare island in a lake called Tere-Khol, located in remote south-eastern Tuva – and nobody has much of an idea why it's there. So we haven't got it all figured out.
some hypotheses though. The structure – likely built in 757 AD in the architectural style of the Chinese T'ang Dynasty – might have been a palace complex for a Buddhist monastery, an astronomical observatory or – as one geoarcheology study seems to think
– an isolated fort for exiled members of the syncretic religion of Manichaeism
– though it was probably never occupied. Probably a good thing since it lacks any of the rudimentary heating systems available at the time. Gets chilly at the Mongolian border. The Siberian Times has the whole story