40-minute boat trip on the Thames from Windsor

French Brothers, a Thames passenger-boat company, departs from Windsor Promenade, the riverside walk, on a short 40-minute trip: it goes up to Boveney Lock and back, passing Eton College, the racecourse and Brocas Meadows. The view of the castle from the river is the best there is.

It has commentary, a bar and toilets on board, and boats leave frequently during the day, so it fits in between other visits. For something longer there are two-hour cruises with lunch. Check the sailing days on their website, which change with the season.