Altar of the Deep God (2014)

From the Introduction

The deep god is not like any other god. It is a primeval force from times before times. For this reason its altar is not just a block of stone. Indeed the altar is consists of the gigantic remnants of an ancient monolith out in the murky water of the rocky reef. Many creatures venerated the old god here and made bloody sacrifices. Very few of them were even remotely human. Although the fishermen of the nearby villages do not really understand the power they toy with they still bring victims to be sacrificed quite regular. They get shipped out here by boat and are herded up the stairs cut out of the stone to be chained to the large standing stone circle. Only a few torches illuminate the scene with their flickering light. And once the alien tentacles begin to rise from the murky depths to snatch the latest offerings anyone foolhardy enough to watch the scene will wish there was no light at all, as nothing seen can be unseen.