Eynhallow Sound is a seaway lying between Mainland Orkney and the island of Rousay in the Orkney Islands, Scotland. The tidal indraught is "scarcely felt beyond a line joining Costa Head and the Reef of Quendale". An Iron Age broch, Gurness, has a strategic outlook over the Eynhallow Sound.
References
Eynhallow Sound Wikipedia(Text) CC BY-SA