Redbone Castle is an island in the middle of a lava lake located at the end of Hellgate. This castle marks the entrance to Draconia, and it's guarded by Demon Skeletons, Skeletons and Ghouls.
You see a sign. You read: Redbone Castle Damnation to all who dare to enter!
Three demon skeleton guard the doors of the building. In the past the Demon Skeletons were being surrounded of protection zone, so you had to kill them from distance with spell runes or distance weapons (which was very annoying for knights). Nowadays, only one Demon Skeleton remains, you don't have to kill it anymore.