Civita Di Bagnoregio

Civita di Bagnoregio was founded by Etruscans over twenty-five hundred years ago. The town is noted for its striking position atop a plateau of friable volcanic tuff overlooking the Tiber river valley, in constant danger of destruction as its edges fall off, leaving the buildings built on the plateau to crumble. The city is also much admired for its architecture, some spanning several thousand years. (wiki) 

Civita di Bagnoregio is also called the "dying town" and you can reach it only walking till the end of the long bridge you can see in the image. There is still someone living there. They go up there with mopeds or carts.
If you are visiting Lazio (Italy), I suggest you to pay a visit to this town.