In several places across the world there are mysterious tracks in limestone soil. These are several decimetres deep and have a tapered shape. Often there are two tracks side by side, but in most cases they are not parallel which makes it likely that a cart would get stuck. In several places in Malta you'll find these tracks, but the most prominent site is Clapham Junction, named as such because it resembles the railway yard of Clapham Junction in London. These tracks can also be found on Sardinia, in Spain and in Bolivia. Those in Bolivia, on the hill of El Fuente have a specific design and are carved into rock.

When and by whome these ruts were created remains a mystery. 

For more information, see Zammit (1928) and Von Daniken (1980).