http://h2zkj5xeycxb2esnyqeabuuo6ui6jlkdb72qjfi2hu3y3h5ilpmjphid.onion/wiki/LocalTravel/index.html
This makes it good value to go from one side of the city to the other, but if you change buses you have to buy a new ticket on the second bus. If you will be taking more than two bus journeys in a day, you should instead buy a Day Ticket (currently £2.30), giving you unlimited travel for the day.