Kakariko Windmill

The Kakariko Windmill refers generally to both the interior and exterior of the windmill in Kakariko Village. The windmill houses Guru Guru, an exit from the village graveyard (which can provide access to a Piece of Heart) and oddly enough, an almost-useless secret passageway which can be accessed from the village area with the hookshot. Here, a cucco is located-to help access unreachable rooftops. At certain points of the storyline of Ocarina of Time the windmill ceases to operate and can be restored (although often temporarily) by embarking on the Song of Storms sub-quest and playing this song on the ocarina.

There is a similarity between the principles of the windmill in Ocarina of Time and the ferris wheel in The Wind Waker (Windfall Island)-although in the latter, Link must change the direction of the wind to activate the sails of the "windmill" as opposed to creating a storm.

Windmill Hut
The Windmill Hut, and known as "?", is the interior of Kakariko Windmill and home to Guru Guru. It is connected to Dampé's crypt, and draws its power from the well. Link can teach and learn the Song of Storms to/from Guru Guru here. Basically, Adult Link is taught the song by Guru Guru (who claims to have learned it from a horrid little Ocarina kid). Then by traveling back seven years, Link then goes and teaches the tune to Guru Guru in the first place.

Dampé's grave leads to the Organ grinder's windmill.

The Windmill is also in Oracle of Seasons, though more as a cameo. Guru-Guru plays a role in the trading game for the Noble Sword.

The music playing in the Windmill Hut is what the Song of Storms is based on. It may be heard here.

Trivia

 * If Link were to hang out in the Windmill Hut and stand still for a while, he will sneeze.