When Clark finally united the Fire, Water, and Air Elements on the Altar in "Commencement," their power was unleashed.
The Elements melded to form a solid diamond shaped like the famous S-shield.
The diamond floated into the air, and when Clark grabbed it, he was transported to the arctic.
Clark threw the diamond into the snow, and it created the Fortress of Solitude-- Supes' headquarters and Earth's repository of Kryptonian knowledge. This shot, a closeup of the diamond flying through the air, was the closing image of Season 4:
Here are some shots of the Fortress, courtesy of [REFERENCE???]: are some shots of
