In the Catacombs, in the ground-level chamber just before the outside area with the cartwheel skeletons (the one with two bow-wielding skeletons), there are two white, floating circles/rings.
Can anyone tell me what these are and what the are for?
EDIT: Here's a screenshot:
This is one of the two rings. The exit on the left of screen takes you to the outside area with the skeleton wheels. The rings are not visible when you first enter this area, but appear after you have cleared the room of enemies. They also don't seem to appear unless you are playing online.