Sol

In Twilight Princess, a Sol is a spherical object that lights the Twilight Realm, similar to the sun of the World of Light. It is made of pure power and is the source of life for the citizens of the Twilight Realm, as well as the source of power for various pieces of Twili technology. The light of the Sols can cut through Zant's dark fog, which is made of Shadow Crystals, and without it, the Twili gradually transform into beasts. Later in the game, the light of the Sols is transferred to the Master Sword to create a "Light Sword."

The two Sols that need recovering are in the Palace of Twilight: one in the east wing, and one in the west. When Link tries to remove a Sol from either wing, Zant's Hand will pursue. If Zant's Hand manages to take the Sol from Link and travel back through the portal in the wall it uses to travel from room to room, Link will need go all the way back to the chamber where he found the Sol originally and try to escape with it again.

Bringing the two Sols to the Pedestals of Light in front of the Palace of Twilight enables their light to be infused into the Master Sword. Placing a Sol on special pedestals can cause platforms and steps to appear. Bringing a Sol near a cursed Twili will cause the Twili to revert to its original form. Curiously, if any Twili are left in their transformed state when both Sols are returned to the Pedestals of Light, they will revert to their original form regardless of whether or not Link brings the Master Sword to them.

Trivia

 * The word "Sol" originates from the Latin word for the Sun. Sol and its derivatives are still used in a number of modern languages.
 * In Germanic mythology, Sól is the goddess of the Sun.
 * In the Spanish version of the game, a Sol is called "", which is the Japanese word for "Sun".