Tales of the underground. I never knew moats were used to prevent people from digging tunnels underneath your walls! - Amit Patel from Bookmarklet

Play Terrarria and feel the pain of mining into water accidentally - Rob Shillingsburg

I've felt that pain playing Dwarf Fortress! :) I had built an underwater farming area (protected from invaders) and had tried building an irrigation system that involved controlled draining of the lake above. Unfortunately I got it wrong, accidentally dug into the surface level, and the entire lake emptied into the 2nd level under my fortress, flooding everything until I hurriedly built a wall to block off part of the area. - Amit Patel

Was that Lake Peigneur? ;-) The first image in the Mine/Countermine section of that article looks like St Andrews Castle. The mine was rediscovered relatively recently when someone was renovating a basement in a house across the street. Now you can explore most of the tunnel from the castle side. - Seth