The first pick up is in Calella de la Costa, the final stop is at Tossa de Mar and every town in between is visited. Most of the boats have underwater viewing areas so you can watch all the fish, and on one occasion a scuba diver complete with fishing spear, as they go by.
It costs €30 per person for a round trip, there are currently no single tickets available, and you will only be allowed to get off the boat (on your return trip) at the stop where you originally boarded, which is good in a way, as it would stop anyone who has oversampled the local hospitality getting lost, but not so good if you fancy exploring.
More information can be found on the Dofijets website.
Unfortunately, whilst all boats go to Tossa de Mar, not all boats come back to Calella, even in high season there are only two stops at Calella, so what I tend to do, is get the train to Malgrat de Mar and catch the boat there, if you do then want to come back early, you have more options with regards to time.
Photo courtesy of en.costabrava.org