Arms of the Sea, by Deeranger

[spneldritchmod.livejournal.com]

Summary:

A peculiar case involving what appears to be human sacrifice in Bandon, Oregon, has caught the attention of the Winchester brothers. It's a race against time and they decide to split up to cover more ground. And so, while Dean interrogates witnesses in town, Sam heads down to the beach to investigate the sacrificial site. There, he stumbles on a weird symbol etched into the rocky cliffs right outside a sea cave... And of course, he has to check it out. Things only go downhill from there.

https://archiveofourown.org/works/59466136