Skull keys

Skull Keys are a more advanced form of lockpick. 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 always breaks after a single use. Nonetheless, these are a must have for every adventurer, because with them even non-magic users can open magic locks.

History
In Ultima V, Skull Keys were very important to enter Stonegate and get the Crown from the Palace of Blackthorn, since in these areas, magic use wasn't possible. A special tree in Minoc grew Skull Keys every day, allowing the Avatar to stock up on them.

The only other appearance of a Skull Key was in Ultima VII. Found on a small island west of Trinsic, it replaced Lockpicks, and never broke.

Trivia
They were available in Ultima V from only two locations:
 * A tree stump in Minoc, which Shenstone frequented.
 * From Kristi at Serpent's Hold. It is possible to get more than 5 keys from Kristi. So long as you never give her your name, you can keep asking her for keys.