The Estación Astronómica Muisca dates from the early centuries AD and was used by the Muiscas to determine the seasons. This Stonehenge-like site contains 115-odd cylindrical stone monoliths sunk vertically into the ground about 1m from each other in two parallel lines 9m apart. By measuring the length of shadows cast by the stones, the indígenas were able to identify the planting seasons.
Because of the phallic forms of the stones, which were carved to represent fertility, the prim Spanish colonialists named the sight 'infiernito' or little hell. The site is 2km north of El Fósil. There's no public transportation, but you can walk here from the fossil in 25 minutes. Alternatively it's accessible by bicycle, horse or taxi from Villa de Leyva.