Graveyard Key

The Graveyard Key is an item that is eponymously described: it gives entrance to a graveyard or one of its sections in Oracle of Ages and The Minish Cap.

Oracle of Ages
The Graveyard Key is found a secret cave in the southern part of Yoll Graveyard. It is needed to open a gate in the northern part of the graveyard, in order to then access the eastern part and reach the Spirit's Grave.

The Minish Cap
Dampé the gravekeeper gives the Graveyard Key to Link while he is traveling about the Royal Crypt region of Hyrule. As Link steps out of Dampé's house a crow steals it. By killing the bird in this same area, Link is able to reacquire the key and open the locked gate.