Lummelundagrottan (Swedish for "The Lummelunda cave") is a nature reserve located near Lummelunds bruk north of Visby on Gotland, Sweden. It is best known for the actual cave Lummelundagrottan, also called Rövarkulan ("The Den of Robbers"). The reserve is 17 ha (42 acres) and include the cave and an area above the ground. It is one of the longest caves in Sweden; the investigated parts of it measure almost 4 km (2.5 mi).