A Map to Where?

The crudely-drawn map reveals nothing of its maker, but it appears to have been drawn with an unsteady hand. Wavering lines and symbols depict a small pavilion with broken columns located to the west of a partially submerged tower. If the map is to be believed, this cluster of ruins appears to be located on the eastern coast of the island. You have no idea what you'll find, but it was important enough for the map's creator to record.