Bath is a small city that and you can walk between any of the main tourist attractions within 10-15 minutes. The tour buses are expensive, noisy, smelly, have to stick to the one way systems, and so are indirect.

You don't get the same views from a bus as you would on foot. The best way to see the Circus is to stand under the trees in the middle, and try clapping. You get a really big echo from all the surrounding buildings. Likewise, the Royal Crescent is best seen first from the Victoria Park, and then along the pavement. Trundling along cobbles on the road just isn't the same.