Belle Isle, the largest of Windermere's eighteen islands, holds the most unusual house in the Lake District: a perfectly circular Italianate villa built in 1774 — England's only round country house in plan, with a domed central hall lit by a rooftop lantern. The Curwen family bought and lived on the island for over 200 years; it has changed hands several times in the 21st century but remains in private occupation.
You can't land on the island, but the lake cruises pass close enough on the route between Bowness and the southern lake for a clear view. Look for the round house through the trees; the island's wooded shoreline hides most of the buildings, but the white walls and the slate dome are unmistakable on a clear day.