Aldeburgh's Martello Tower stands on the shingle between the River Alde and the sea, a short walk south of town. Built in the early 19th century as part of Britain's anti-Napoleonic coastal defences, it has an unusual quatrefoil shape and feels wonderfully exposed.
The Landmark Trust owns the tower, so you usually see it from outside rather than touring the interior. The walk out is the point: beach, river mouth, wind, and a lonely military relic at the end.