Dark Barrier

From Zelda Wiki.org

Appearing only in Four Swords Adventures, these Dark Barriers are created by Vaati, and block the exit from every level. The barriers can only be broken by powering up the Four Sword, which is acheived by collecting 2000 Force Gems within the level. The barriers are always composed of four glass globes containing the eye symbol of Vaati, connected by a chain of electricity.