Although it shows on the map, this is one of those hard-to-get-to locations. The AA mob Remia Starshifter stands in here with two helpers. We got here from the Crimson Crown, using the stone "bridge" second to the right (clockwise) from the bridge to the coffin area. There is a short, narrow ledge to the right at the outer end, and when you start falling you can direct your path into the room. When we went in the mobs stood far enough back that we did not aggro them when we landed, giving us time to get situated. Watch out for the fleshgoyles that patrol some of the bridges in the area.
We found it in the normal version of the Crypt even though it's listed under Vengeance. NOT the Eternal Twilight version--the room would still be there but Remia may not.