For The Legend of Zelda: Ocarina of Time on the Nintendo 64.

Equip the Lens of Truth and the Ocarina. Play the Song of Storms, and activate the Lens the moment the song ends. If you time it right, the Lens of Truth will not consume any magic. The effect ends when the Lens is deactivated. This can be done anywhere, but remember that the Lens automatically stops being used when you open doors or do other actions.