Don't miss Skottvangs gruva, the historic mining area a bit north of Gnesta.
The iron ore mining took place her since 13th Century.
Every summer the "Charcoal week" is held at the mining are when the ancient charcoal burning will take place in a traditional charcoal pile.
There are a lot of ancient remains from the viking era in the region of Sormland.
If you are interested in history you should explore the rune stones and rock carvings around Gnesta.
More info at the local tourist information office.
There is a cave close to the Klubba church at lake Baven west of Gnesta. The cave is accessible through several cracks in the rock. The biggest entrance reminds of a church entrance. If you want to enter don't forget a torch.