After resting and recuperating and recovering spells and casting protective enchantmnets, the party moves across the blasted yard past the site where they fought the undead.
At the center of this area, pounded down into a wound in the earth like a spike pounded into flesh, stands a black tower gleaming with the sheen of a black adamantine alloy. The earth seems to recoil from the touch of this strange structure, so it is surrounded by the gaping trench of this wound, its black walls plunging downward out of sight. Cracks, exposing red hellish light from below, start at the wound and cross the blasted yard. No windows exist on the tower and the single door is accessible only via a narrow span bridge crossing over the wound.
The inner walls of the crater and the black tower rise over two hundred feet above you.
Sulfuric smoke is thick around the bridge, rising out of the cracks between the volcanic stone and the black Adamantine spike. Down below, you can see lava some sixty feet below the bridge.
The bridge is ten feet wide and made of a black iron alloy. The door is made of solid adamantine. No door handle or other method of opening the door is visible.