Cross

The Cross is an item in.

Location
The Cross is found in the sixth palace, Three-Eye Rock Palace. Unlike the other items in the game, it is guarded by a mini-boss: a Rebonack. After its defeat, Link gains a key and proceeds to take the Cross from a pedestal in the next room.

Uses
The Cross, while useless in the dungeon where it's found, allows Link to see the dangerous blue-colored Moas that infest the graveyards in East Hyrule, the town of Old Kasuto, and the Valley of Death (which itself serves as the path to the Great Palace). It should be noted that, with a lot of skill, it's possible (albeit difficult) to survive those places without seeing the invisible enemies. A more risky method involves the constant use of the Fairy magic.