The Pit of Saron is the east-wing of the Icecrown Citadel dungeon.  The video below is an exploration of the pit which has plenty of trash mobs: necromancers, gargoyles, Vrykul, Iceborn Proto-drakes, skeletons, undead orcs and frostwyrms among other mobs.  The pit looks similar in size to Obsidian Sanctuary. The three bosses are: Scourgelord Tyrannus (Frostwyrm), Forgemaster Garfrost and Ick and Krick. Check out some of our screenshots here.