venice

Yes. There are two, though. One at Piazzale Roma and one on the Tronchetto. The signage is good as you come across the bridge and there's really nowhere else to go.

Is one better or cheaper then the other?

There actually more than one in Piazzale Roma. If the first one on the right is full, continue forward and there's another garage behind it. The ones on Piazzale Roma cost 24 euro a day, Tronchetto I believe is 21 euro a day in the garage. I personally much prefer PR as Tronchetto is on a man made island so you pretty much have to take the vaporetto to reach Venice proper (and back to your car) whereas the garages on PR offer the convenience of getting out of your car and walking right into the heart of Venice as wel las leaving when you want to leave without having to wait for a vaporetto (not to mention buying the vaporetto tickets). If you want cheaper parking, you can park in Mestre, right across the lagoon on the mainland and take a train or bus in.

Having parked there once. I would park on the mainland and catch a ride in. It wasn't hard to find parking. When you get to the end of the bridge you either park or turn around. We chose a private parking garage because we were worried about security. The good thing was our car was in one piece when we retrieved it; the bad things were it was expensive and took better than an hour to park and more to retrieve the car.

Ive parked on the island and also in Mestre. I much prefer Mestre. Its easy to get to, across the street from the RR station.It was less expensive also. I also think it is more secure.

Tronchetto has VIP parking which is 30 Euros a day and your car is behind wall to wall, floor to ceiling hurricane fencing. An attendant has to let you in and out. If your car is valuable you might consider that option; it's on the first floor and the hardest part was figuring out how to get into the VIP: the answer is finding an attendant ( go to the office by the exit to the walkway). We found one attendant patroling the garage on a bicycle.