When you arrive at Port Arthur, you will need to make a decision on how long you are planning to spend here, and which activities you wish to participate in. If you choose and of the three excursions which include a boat ride, you will head down to the ferry pier where this boat will be waiting for you.
The three excursions which will incur a ferry ride are Point Puer where the convict boys' prison is located (about an hour ferry ride), the harbour cruise (20-30 minutes) or the Isle of the Dead cruise (30-hour). If you are going to do all three, it is likely recommended that you stay the entire day.
The ferry is located within 1/2 a mile from the entrance down by the water.
Individual excursions are about $12AUD each for these ferry rides.
Port Arthur is on the Tasman Peninsula, about 60 miles/100 km south-east of Hobart.
Driving is probably the best way to get there if you can rent a car. Allow at least 1.5 hours to enjoy the drive, longer if you want to check out some of the sites along the way (well worth the trouble!). The drive along the Tasman and Arthur Highways forms part of the Convict Trail Touring Route; take in the views of the water and the farm country or stop at some of the vineyards and artist studios.
If a car isn't an option, there are plenty of buses that run all day between Hobart and Port Arthur.
For something really different, take a boat!! The MV Marana, operated by Port Arthur Cruises, provides a ferry service from Hobart to Port Arthur. The catamaran offers enclosed seating for 166 passengers with a full range of facilities including food and beverage service. Make sure you make a reservation - 1300 134 561.
The closest commercial airport to Port Arthur is Hobart International Airport. (HBA) is one of the smallest airports to service a high volume of air traffic passengers, but is very easy to navigate. It is serviced by the major Australian carriers, Qantas, Virgin Blue, Jetstar, and minor Australian air carrier TasAir. In additional, recently it appears Tiger Airways will fly here from Asia.
You can likely make it from Hobart Airport to Port Arthur in 1 hour and 15 minutes, as it is east of the city of Hobart by about 15 minutes.
Most likely, if you are spending more than a day in Tasmania, you will need a rental car. Although there are tour buses that depart from the airports and make the tour around this beautiful little island, the freedom of time and ease of the drive makes a rental car well worth it on this trip.
In particular, I would not want to be held at Port Arthur too long, or conversely not get to see all there is to see because the bus was leaving. Also, there were other sites along the Convict Trail during this trip which would be fun to stop at and impossible in another form of transportation.
Most of the major car rental places have locations in both Hobart and Launceston, and the drive from Hobart to Port Arthur is roughly 1.5 hours at an easy pace.