Goa Tourism's new Hop on Hop Off bus service works like other sightseeing bus tours around the world, currently running on two set routes. The purple route covers the Panaji area, running as far as Dona Paula to the west and Old Goa to the east. The second route operates in North Goa from Fort Aguada to Vagator beach and back. Timetables run roughly from 9am to 6pm but whether they can stick to a timetable in Goa's high season traffic is another matter!
The pass is valid for two days and you can get on and off at any of the designated stops along the way.