Blasted out of solid granite by soldiers in the 1960s, this V-shaped arc of sea tunnels was designed to protect boats from bombs during the war years. Approach it through a large garden displaying two of the landing vessels that once unloaded here, then descend to a pair of subterranean waterside walkways serenaded by classical music.
Both tunnel ends are now blocked to the sea, so the water inside is completely still and offers mirror-like reflections. If you have time, after exiting it's worth strolling 250m back to the coast using the 'Seasight Trail'. The rewards are fine views of the very scenic rock-and-forest coastline.
Some bus 6/6A services come this way or you can use Tourist Bus A.