It was called River Red Rover,unlimited 24hr travel on the river from Westminster-Waterloo-Tower-Greenwich. You could get on and off where you wanted, there were facilities on the boat and there was a running commentary explaining where you were and what the surrounding buildings were, it was lovely, enjoy!! I would say that it may be difficult to access the boat if you have mobility issues, although I suspect they would probably sort this for you, but you would have to check with the provider.