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
The forebears of the Britannian skull keys started to appear on Earth, as the intrusions of time wrecked the planet of the Stranger. Although it is bearing the same name as the Britannian invention, it was used to unlock airplanes and allowing entry to aviators.

It was until during the tyrannical regime of the once noble regent Lord Blackthorn, these particular items came upon Britannia. A brilliant smith called Shenstone invented the more advanced skull keys, an important tool which can open doors who are magically locked. Strangely enough, they disappeared in years afterwards.

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 II
Skull keys may be found at the following locations in Ultima V:
 * The Stranger has to fight Thieves to get them.

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.
 * Serpent's Hold (Sold by Kristi for 100 gp)

Trivia

 * Kristi can supply skull keys indefinitely, provided she is never given the Avatar's name.