One of several caves in The Witcher, the swamp cave is located in the southern part of the Swamp just off the road through the forest. The entrance is guarded by echinopsae. The corpse outside is not a great omen. There is a campfire, so it is not all bad, but be sure to clear out the drowners and drowned dead before trying to meditate there. In Chapter II, wolves are found there. In Chapter III, there are cockatrices and much more.
There is also what appears to be a burial chamber with a vran's sarcophogus surrounded by large obelisks that flank a path leading down to the Circle of Hanging Stones, a circle of elements for the sign Quen. The sarcophagus contains one of the sephirah as well as a nice axe.