Blue Field Passage Gem

The blue field passage gem is an artifact which allows its bearer to pass through the magical barriers en route to the Hall of the Mountain King unscathed. It appears in  Ultima VIII.

Description
The inner sanctum of Lithos was defended by a number of magical traps and barriers, including an elaborate maze consisting of blue force fields. This was done so that only the best would go on and join the Necromancers to serve him. Should the Avatar retrieve this gem after getting through the maze of force fields, they could pass through these fields unharmed, making passage back through the labyrinth to the door deeper into the halls an easy task.