Nestled between Northumberland’s sweeping sand dunes and Yorkshire’s characterful seaside villages, Seaham is one of north-east England’s most rewarding coastal escapes. Part of Durham’s Heritage Coast, the former harbour town lies just 13 miles east of the city of Durham and six miles south of Sunderland, with cliff-top trails, wide beaches and sea views. Seaham’s fortunes were transformed in the early 20th century when the 6th Marquess of Lon…