So, I just obtained the watchtower basement key from the butterfly boss in NG+, I go to unlock the door (the one opposite from the red dragon guarding the bridge) and it just won't work, keeps saying "It's locked". I've double checked to make sure it was in my inventory and everything. Is my game glitched or am I at the wrong door to use this key?
I could be wrong, but I'm pretty sure the watchtower basement key is the one that leads to Havel. The key you are looking for, which leads to lower undead burg and the depths, is the key that is on the other side of the big gate in undead parish.