We have moored in Bordeaux 3 times. It’s a fantastic place to stop. The journey downstream from Castets-en-Dorthe or back is about the same: the tide carries you both ways. It takes just under 4 hours. You need to have a reservation on the pontoon. Moorings are secure, with a locked gate from the quayside. You are right in the centre of Bordeaux and can walk or take a tram to anywhere in the city.