I was in Throne of the Tides when it was current content. On the way to the shaman boss on the right hand path, my character got knocked back and it glitched through the floor and landed in a zone entirely underneath the dungeon. It was a massive area fully modelled and with solid terrain that I was able to explore. There was a road to follow and lots of structures in the distance. There was a massive pit in the centre of everything that I wasn't brave enough to jump into incase I died. I was underwater but there were no water physics or breath meter. I'm totally guessing but I believe that it was the W.I.P for the underwater raid that ultimately got scrapped. This would have been in 2010 or 2011 and it never dawned on me to take screenshots because I was worried about being kicked from the dungeon group. I wouldn't have had the capability of recording video in that time period. I assumed it was a common glitch to happen and that it would occur again. It never did.