Tattershall Castle is a 15th-century red-brick keep built above the Lincolnshire fens by Ralph Cromwell, Treasurer of England, to display his power, and one of the earliest and finest examples of medieval English brickwork. Its huge Gothic fireplaces were torn out for sale to America before Lord Curzon of Kedleston bought the castle in 1911, recovered them and left it to the National Trust. Climb the 149 steps through seven storeys to the battlements, where the view reaches from the Fens to the Wolds and, on a clear day, Lincoln Cathedral; look for centuries of graffiti carved in the stairwell and explore the double moat and dovecote outside. Reviewers single out the friendly guides, the craft activities for children and the cellar. Tips from visitors: there is no cafe, only drinks and snacks at reception, so bring a picnic; the toilets are near reception, not in the tower; and dogs on short leads are welcome in the grounds only.