Stone of Trials

The Stone of Trials is an item from Skyward Sword which gives Link access Sky Keep.

Location and Uses
Link is rewarded with the stone after completing the fourth and final Silent Realm, the Goddess's Silent Realm located in Skyloft. The Stone is one of a pair, and when the two are reunited the way is opened to Sky Keep beneath the Statue of the Goddess. The identical stone is lodged in a one-eyed bird statue located on Skyloft near the entrance to the Waterfall Cave. When Link inserts his stone into the empty eye socket, the bird statue turns around, opens its beak and fires a cannon ball at the Isle of the Goddess. Eventually, begins to shake and the bottom of the island breaks apart, unveiling the Sky Keep. The bird statue then spits out a number of orbs with clawshot targets which Link, with his Clawshots, uses to reach Sky Keep.

The statue that holds the Stone of Trials turns 180 degrees at night, rendering it impossible to open Sky Keep unless it is daytime.