Ultima II: The Revenge of the Enchantress/Pangea age

Dungeons and towers

 * In 1423 BC, in Castle British, the subdued balron whimpers: Lithium packs the 16th level!

Tri-lithium is necessary for space travel.

In the original version of Ultima 2, dungeons and towers are completely optional, because tri-lithium can also be dropped by defeated thieves.

In the Japan-only FM-Towns port, enemies do not drop tri-lithium anymore, therefore there is a reason for exploring dungeons and towers. Still, 20 tri-lithiums are sufficient to visit all the planets and come back to Earth.

Because of the 99-rollover mechanic, collecting 100 tri-lithiums is the same as collecting zero.

OPTIONAL: dungeon in Greenland
In the DOS version of Ultima 2, this dungeon cannot be accessed in Pangea.