Basement Key

In Game Description

Opens the narrow passage leading below
at the far face of the great bridge in
the Undead Burg.

The lower Undead Burg is a treacherous place.
Do not turn your back on the wily thieves, or
the wild dogs who serve the Capra Demon.

Availability

Found on a corpse on the stairs leading up to the church in Undead Parish, next to the lever that opens the gate back to the area with the Armored Tusk

Opens

The door near the bridge with the Hellkite Dragon that leads down to the lower section of the Undead Burg