This property, formerly the grounds of the Port Arthur Penal Settlement, is now a lovely—and quite large—historical park with a fascinating convict past central to Tasmania's history. Be prepared to do some walking between widely scattered sites. Begin at the excellent visitor center, which introduces you to the experience by "sentencing, transporting, and assigning" you before you set foot in the colony. Most of the original buildings were damaged by bushfires in 1895 and 1897, shortly after the settlement was abandoned, but you can still see the beautiful church, round guardhouse, commandant's residence, model prison, hospital, and government cottages.
The old lunatic asylum is now an excellent museum, with a scale model of the Port Arthur settlement, a video history, and a collection of tools, leg irons, and chains. Along with a walking tour of the grounds and entrance to the museum, admission includes a harbor cruise, of which there are eight scheduled daily in summer.
There's a separate twice-daily cruise to and tour of the Isle of the Dead, which sits in the middle of the bay. It's estimated that 1,769 convicts and 180 others are buried here, mostly in communal pits. Ghost tours (reservations are essential) leave the visitor center at dusk and last about 90 minutes. Buy your tickets at the site, or at the Brooke Street Pier, at Franklin Wharf in Hobart.