Detailed information about practically everything worth seeing and interesting in Karlsruhe. It's a lot of fun, especially when the weather is nice in the open-top bus. However, the "hop on hop off" is very limited, since the buses only run three times a day. So you can practically only get off twice if you take the first bus of the day and then continue on the next bus. Or you can take the last bus and then the first and second the next day (only works on weekends).