Star Waste Catacombs in Elden Ring

Once inside, activate the place of grace and run down. Destroy the flowers, follow even lower and pass by a huge flower in red rot. You will enter a crypt with a pillar in the center. Go around this column to see a niche with a statue and a lever. Pull the lever to open a heavy door somewhere. Note that the first interaction will trigger a trap, so it's a good idea to move back.

As for the heavy door, it is located directly opposite the niche with the lever. You need to destroy the Shadow of the Cemetery. Reward - Rot Kindred Ashes .