An antique ring is an item used in the Unhappy ghost puzzle while Dungeoneering. The ring must be returned to the jewellery box in order to proceed. After you have fixed the broken pillar and pot, returned the ring to the jewellery box, and opened the coffin and blessed the remains, all the doors in the room will be unlocked and you can proceed further into the dungeon.
Although it is a members object, the ring can be obtained by F2P parties who happen to stumble upon the unhappy ghost room. However it has no function for them as they cannot pass the room.