Tears of the Kingdom
The Forgotten Foundation is first seen, though not named, in the prologue to Tears of the Kingdom. Link and Zelda travel through it in search of the source of gloom afflicting Hyrule. In the process, they happen upon a series of Zonai sculptures and murals, which lead Zelda to become very excited and start snapping pictures with her Purah Pad. Three of the mural panels in the final room are covered in sediment, a point which is not remarked upon at the time. Link and Zelda then pass through to the Imprisoning Chamber, leading to the revival of Ganondorf and the Upheaval.
When Link returns to the Forgotten Foundation much later, on the quest to Destroy Ganondorf, he can break the sediment, revealing three additional panels which all show Zelda.
All the panels from the final room, as shown in the credits sequence, represent:
The wedding of Rauru and Sonia
First half of The Demon King's Army
Second half of the Demon King's Army, including Demon King Ganondorf himself