The Chaos Druid Tower is located to the north of Ardougne and is home to 4 chaos druids, located on the ground floor, who can be killed for good experience. The door is locked and requires level 46 Thieving to open.
The tower also houses the entrance to a dungeon containing a chest (formerly two), requiring level 59 Thieving to open and holding two blood runes and 500 coins, granting 250 experience. Once a player has successfully opened the chest and removed its contents they will be teleported, along with their loot, to a house in the north of East Ardougne. The chest respawns every 210 seconds or 3 and a half minutes. The dungeon itself is also inhabited by 5 giant bats and 7 ogres.
Attempting to open the chest is required for the Ardougne Hard Task "Blood Bank Withdrawal".
Note that to open the chest safely, one must right-click and choose the "Check-for-traps" option. Simply left-clicking on the chest will trigger traps which can do up to 1600 damage.