Watchtower Basement Key

In Game Description

Key to the basement of the watchtower in
the Undead Burg.

The basement of the watchtower forms a stone
cell. There are rumors of a hero turned
Hollow who was locked away by a dear friend.
For his own good, of course.

Availability

Found on the body of a dead smith after defeating the Moonlight Butterfly in Darkroot Garden

Opens

Door¹ leading from the bottom of the Watchtower in the Undead Burg's main section to the Darkroot Basin

or, if you're coming the other way,

Opens the tower door next to the lake in Darkroot Basin, which leads directly to Havel the Rock's lair in Undead Burg

Footnotes

1. Having the Master Key unlocks this door also