Choosing a Path:

Go down the stairs where an Imp will drop from above. After defeating it, you’ll have two paths to Elden Ring Runes choose from:
East Path: Two Imps guard a corpse. After defeating them, loot the corpse for the Ancient Dragon Knight’s Cookbook 1.
West Path: Head west, and as you descend the steps, the spiked ceiling will collapse again. You can either wait for it to lift or jump on top of it as it rises.
Top of the Ceiling:

Get on top of the ceiling and run across to reach a platform with a Yellow Fulgurbloom and a corpse containing x3 Knot Resin.
Wait for the ceiling to rise again, then run across it to reach the room to the south.
Defeat the spellcaster and head upstairs to the east to face two Messmer soldiers and a black knight. Lure the soldiers away to deal with them separately, then sneak up behind the black knight for a visceral attack.
Looting and Backtracking:

After clearing the room, pick up the Great Ghost Glovewort from the floor.
Backtrack to the earlier section with the spiked ceiling, drop down onto it, and wait for it to rise. Time it correctly to drop down and enter the tunnel to the east, where another Imp will ambush you. Loot a Yellow Fulgurbloom in the process.
In the northwest corner, climb a ladder to Elden Ring Runes buy reach an earlier section of the dungeon.