After defeating Melchiah and exiting the corresponding area, Elder God says: With Melchiah's gift your way is opened. Return to the seat of Kain's ill-omened empire. It's sterile silence has secrets yet to unveil. But I'm not that much familiar with the game world locations, so I'm not sure where to look.
Go after killing Melchiah
soul-reaver
Best Answer
You need to go to the area with a wall and doors in it. This area is one of the first you visit. It's just beyond the area with the first two enemies in physical realm in a room with light coming from the ceiling and the first cube puzzle. When you first visited it, there was a dialogue sequence between Raziel and the voice of Elder God.
This area can be accessed through the "vortex under bridge" gateway, and you should go away from the bridge to reach it.
The last door in the stone wall is a grate that you can now pass through using the new power gained from defeating Melchiah.