Nearby to the previously posted Machu Picchu, Peru, is a very unusual archaeological site - the strangely beautiful Inca ruins of Moray.

The concentric rings clearly visible were farming terraces with a sophisticated irrigation system, constructed inside enormous natural depressions in the landscape. Supposedly the Incas built them here to experiment with the different farming conditions the landscape accommodates, as the annual temperature difference between the top and bottom can be up to 15°C (27°F).

Which is fairly impressive given that even this largest depression is only 30 metres (100 feet) deep.

Here’s the very brief Wikipedia page.

Thanks to Josh E.