Ooooo. I did a small one of those. Normally, they're expensive and you ride up quite a ways up the river and back. But there were alternate ways of doing it. They have boats that were smaller and different companies originated at different locations. Then they would travel up and down the river like a bus. You can get a ticket for let's say 8 stops up the river. Then you can get off at any of the stops and sightsee, get back on with the same ticket and go further up the river. You can get on and off as many times as you want between the furthest point up the river you paid for and your origination location. The only trick is, you have to time your return trip to coincide with the last boat coming back, or else you'd be stuck at a stop without your car until the next day. Not as elegant as the expensive cruises, but you got to see a lot just the same.
I'd do it again if I had the chance.