Lummelundagrottan in Gotland

You're standing at the Lummelunda Cave, about thirteen kilometres north of Visby on Gotland. First, look at the steep limestone cliff, known here as the Klint. Right there, by the old mill called Överstekvarn behind Lummelunda Manor, is the entrance to one of the longest caves in Sweden. Almost four and a half kilometres of it have been explored so far.