Isle of Lost Souls

Across the Causeway of Fiends lies the Isle of Lost Souls, which is avoided by all sea vessels. In a radius of roughly 10 miles, it is said that the very rocks of the sea bed will rise and hole any vessel approaching more closely. Further, any lost at sea will become bound to the isle as ghosts, tormented by unknowable horrors for eternity. Sailors will jump overboard into stormy seas with a prayer to Procan for their souls rather than enter these waters. Intelligent sea dwellers such as sea elves, selkie, or dolphins warn ships away from the area.
The isle itself appears only to have the ruins of an ancient monastery or mansion house atop its sheer cliffs, but distant scrying reveals an intensity of evil and magic beneath that site which is powerful enough to threaten insanity to the diviner studying the place. In texts which are now no more than a rumor in the night between old sages, the place is said to be the last resting place of three of the greatest of the Ur-Flannae. If this is true, the perils below it do not bear even thinking about.