[cf. Ir. sídh].
Another name for the otherworldly Annwfn, especially when seen as an elysium. Sickness and old age are unknown in Caer Siddi. Enchanting music is heard there, and a fountain flows with a liquid sweeter than white wine. Gwair was kept in a well-equipped prison here. Caer Siddi is sometimes identified with the islet of Grassholm off Dyfed (until 1974, Pembrokeshire), as is Gwales. See also CAER FEDDWID.