Giant's Causeway, Ireland

The Giant's Causeway is a grouping of about 40,000 interlocked basalt columns, fused together during a volcanic eruption in ancient times. This World Heritage Site is located about two miles north of the town of Bushmills, on the beautiful Irish coastline.

There are many tall yarns in Irish folklore about how the Giant's Causeway was formed, and most of them involve warring giants, which seem to be a common thing in their "historic tales" ... I'll let you dig through those on the wikipedia page concerning the legends of the Giant's Causeway.

Chairman Mao's Underground City - Beijing, China

Source: http://www.viceland.com/blogs/en/2009/11/17/chairman-mao%E2%80%99s-underground-city/#more-8124

In 1969, Chairman Mao commanded the construction of a second Beijing beneath the surface of the original city, designed to accommodate all six million of its then inhabitants so that if nuclear war did kick off, folk would still have somewhere to hang out and play Mah Jong while the rest of us burnt to death in a shower of atomic rain. War never came, but the city is still there.