The Legend of Zelda: A Link to the Past/Ganon's Tower

'Originally, the great tower on the west portion of Death Mountain is closed to explorers. Only after rescuing all seven of the maidens and receiving the seven Crystals could one enter the tower. Once you have all seven Crystals, return to Ganon's Tower and the way will open up.'

Ganon's Tower
This impressive structure is said to be where Ganon spent most of his evil reign over the Dark World. Legend says that you can only break the seal of the tower after collecting the seven Crystals which Ganon has hidden in the dungeons of the Dark World. The seven maidens held captive in the Crystals can magically make the seal disappear. You are then free to explore the tower and search for Ganon. But you won't find this master of evil until after you survive battles with four creatures that you have already encountered in the Light World. Your long journey is close to completion.