ArenaNet have dropped more info on how dungeons will work in Guild Wars 2. The world of Tyria will contain eight instanced group missions, made gradually available from level 35 onwards. Each dungeon has a story mode and an exploration mode. Once dungeon's story has been completed, groups will be able to pick their choice of three advanced explorable versions of that dungeon. Each version will come with different challenges, including new boss fights and enemies.
The dungeons are completely optional, but come with their own background and storylines and are packed full of loot. The trailer above sets up the catacombs, inhabited by the ghosts of a dead army, cursed by their jerk of a king to defend the city until the end of time. VG247 have eight minutes of footage of a team battling their way through the catacombs. It also gives us a glimpse of the underwater combat ArenaNet recently revealed. You'll find the video embedded below.