Southwold lighthouse was constructed in 1887 by Trinity House. It stands as a landmark in the centre of the town. It replaced three local lighthouses that were under serious threat from coastal erosion. It began operation in 1890 and was electrified and de-manned in 1938. The lighthouse is unusual in that the light itself is switched on and off in sequence (four flashes every 20 seconds), rather than using lenses to create a rotating beam. Trinity House organises visits during the summer.