Is it the House of Stewards, because no one was actually slain there? Or because it was the only place where someone took their own life, rather than being slain? Denethor killed himself, but failed to bring about his son's death.
Osgiliath - Many were slain in the battles fought there.
Bag End - Saruman and Wormtongue were slain on its doorstep.
Meduseld - Helm's son, Haleth, was slain defending the hall.
Thingol's treasury - Thingol himself died there.
If that's not it, and given that this question has already taken up nearly 2 pages, I would suggest that a BIG hint is in order.
