Pirunpesä, a rocky ravine in Tiirismaa that literally means the Devil’s Nest, is one of the finest geological formations in southern Finland and in the entire Salpausselkä ridge. Pirunpesä is a conservation area, and it has a diverse terrain, with mounds of rocks and plenty of kettles.
Pirunpesä is surrounded by vertical cliffs that are 5 to 20 metres in height in some places, and nowadays the ravine contains a large number of weathered quartzite boulders. The Pirunpesä conservation area is partly green and partly dryish boreal forest. The area covers 34 hectares.
The paths in the area are good to travel even though they are stony and full of rhizomes like most hiking trails. There is a resting place at the start of the ravine valley and a hiking trail goes around the area, with views to lake Vesijärvi, Messilä golf and Lahti city. The area belongs to the Natura 2000 network.