Hadleigh Castle is a romantic ruin on high ground above the Thames Estuary, with broken towers, open grass, and broad views across marsh and water. Its power now lies less in military drama than in the way the ruins sit in the landscape.
The castle makes an easy excursion from Southend-on-Sea, especially for walkers. Bring windproof clothing, take your time with the views, and see it as part of the estuary edge rather than a conventional castle tour.