Fog horns are heard less often around coasts nowadays, because ships have modern technology to help stop them running aground. Still, some of the now-defunct equipment forms interesting sculptural features on coastlines, including the large horn shapes which were needed to project the sound loudly out to sea. However, some fog horns can still be heard, although the old complex machinery has often been replaced by simpler, electronic, automatic systems.
The fog horns at Nash Point lighthouse, South Glamorgan CF61 1ZH, are occassionally sounded – see this website for details. “these went off when we were half a mile away – we jumped more than half a mile ”  (map).
Trevose Head lighthouse was automated in 1995, but the fog horn still sounds when visibility is poor. So if you want to hear the fog horn, you’ll need to get lucky (or unlucky!) with the weather. Roads, parking and footpaths close by. (map).
The Lizard Lighthouse’s twin towers mark the most southerly point of mainland Britain. (map). The fog horn is automated and only sounds in poor weather.
Sally Port Cottage, St, Mawes, Cornwall. map is on private land. The only way to visit this old lighthouse is to stay in it. “You are reminded that St Anthony’s lighthouse is an operational lighthouse and there is an electronic fog signal that operates automatically, ear plugs are provided in case conditions are misty.”  Book through Rural Retreats.
The island of Flat Holm in the Bristol Channel can be accessed from South Wales by boat. A long way to travel just to look at a roof, but the island was also important in telecommunication history, as the world’s first radio transmission across water was made from here. Website. Map.