Last world there was a cave exit leading directly to deep water. If you used it to leave the cave, you'd be swimming in there immediately (hope you don't have a bad connection that takes ages to load the outside map). I'm not sure what would happen if you left there without having the Swimming skill; maybe you'd even drown instantly in that case.
"The psychological trials of dwellers in the last times will be equal to the physical trials of the martyrs. In order to face these trials we must be living in a different world."