Flannan Isles Lighthouse, Lighthouse on Eilean Mòr, Outer Hebrides, Scotland

Flannan Isles Lighthouse is a 23-metre white cylindrical tower near the highest point of Eilean Mòr in the Outer Hebrides, Scotland. Its black-framed lantern room with a domed roof sits above a metal gallery railing, and a flat-roofed white building extends to either side. A stone retaining wall runs in front on a grassy slope.

David Alan Stevenson designed the lighthouse in the late 19th century, and George Lawson carried out construction between 1895 and 1899. Automation later replaced the keepers who once lived permanently on the island.

The name Flannan comes from Flannan Mac Toirrdelbaig, a 7th-century bishop who evangelised the area and retired to Eilean Mòr, where the ruins of his chapel still stand. Shepherds brought sheep to the islands only in summer for the quality of the grass; otherwise the misty, wreck-strewn isles were avoided and called "the seven hunters".

The island can only be reached by chartered boat or helicopter, as the Northern Lighthouse Board controls and monitors access. Anyone planning the crossing should expect rough seas and changing weather, since the islands lie far off the coast.

In December 1900, three keepers vanished without a trace while the lighthouse itself remained untouched and the doors locked. This event remains unexplained to this day, despite decades of investigation and numerous theories.