Silent Realm

The Siren Realm, also known as the Siren World, is a location from The Legend of Zelda: Skyward Sword. It appears to be an alternate dimension.

Story
At certain points in his quest, Link will use the Skyward Sword to enter the Siren Realm. Consequently, Link is unarmed during these sequences. The realm contains guardians capable of killing Link in a single hit, though these guardians can be put to sleep for a short time. In order to complete the trials in the Siren Realm, Link must collect teardrop-like items. These trials somehow function to forge the Master Sword from the Skyward Sword.