The lighthouse has warned passing ships of the treacherous rock below since its completion in 1809.

The 91-foot (28 m)-tall lighthouse on South Stack was designed by Daniel Alexander and the main light is visible to passing vessels for 24 nmi (44 km; 28 mi), and was designed to allow safe passage for ships on the treacherous Dublin–Holyhead–Liverpool sea route.

It provides the first beacon along the northern coast of Anglesey for east-bound ships.

It is followed by lighthouses, fog horns and other markers at North Stack, Holyhead Breakwater, The Skerries, the Mice, Point Lynas and at the south-east tip of the island Trwyn Du.

Visitors can climb to the top of the lighthouse and tour the engine room and exhibition area.