Where is the key to saarthal?

The key to Saarthal is located in the ruins of Saarthal itself, which is part of the "The Eye of the World" questline in the game "The Elder Scrolls V: Skyrim." Players can find it on a table within the Saarthal excavation site. The key unlocks a hidden door that leads to deeper parts of the ruins, essential for progressing in the quest.