Skull keys

Skull keys are a more advanced form of lockpicks. While the common lockpick can only open normal locks, skull keys can also open magically locked crates and doors. They are therefore extremely useful when such a lock has to be opened and the area doesn't allow the casting of the spell Unlock Magic.

Unfortunately, a skull key is only good for a single lock. Nonetheless, it is a must-have for every adventurer, because with it even non-magic users can open magic locks. Skull keys appear in  Ultima V.

History
During the tyrannical regime of the once noble regent Lord Blackthorn, a brilliant smith called Shenstone invented the skull keys, an important tool which can open doors who are magically locked.

Skull keys were very important for entering Stonegate, and for retrieving Lord British's Crown from the Palace of Blackthorn, since in these areas, magic could not be used.

Ultima V
Skull keys may be found at the following locations in Ultima V:
 * A tree stump frequented by Shenstone in Minoc housed new skull keys daily.
 * From Kristi at Serpent's Hold for 100 gp.

Trivia

 * Kristi will supply skull keys indefinitely, provided she is never given the Avatar's name.
 * In Ultima VII, a large key may be found in a small hut on an island west of Trinsic that uniquely shares some similarity with the skull keys found in Ultima V. While this key cannot open magic locks, it can be used anywhere a lockpick otherwise would be, and is unbreakable.