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.
Coordinates: 59°07′52″N 3°04′34″W / 59.131°N 3.076°W