Markings on Adûnaic suggest the existence of a grand shrine somewhere on the island. Perhaps there, you will find answers.

When Revealed: Add 2 copies of Lost Island from the top of the Uncharted deck to the staging area. Add Shrine to Morgoth to the staging area, Lost Island side faceup. Remove all progress from each Uncharted location in the staging area and shuffle them so that the players do not know which one is which.

You search for the shrine, unsure of its exact location...

Forced: After a location is explored, if it would be shuffled into the Uncharted deck, add it to the victory display instead.

The players cannot defeat this stage unless Shrine to Morgoth is in the victory display. When Shrine to Morgoth is added to the victory display, the players win the game.