The Snake Dungeon was a dungeon in the Sosaria of Ultima III. The dungeon was located on an island and reachable with a Moongate on the phase of crescent waxing moon. The Stranger needed to visit this dungeon, as it was the only one in which the Mark of the Snake was available, which granted passage past the Great Earth Serpent and into Exodus' Castle of Fire. The Mark of Kings was also available on level 8.