It sounds like a setup for a joke—landmark Boston jailhouse converted into luxury hotel. While the new Liberty Hotel (215 Charles St., Boston, Mass.; 617/224-4000; libertyhotel.com; doubles from $425) does make all the requisite big-house puns—room service is "solitary dining," the bar is in the former basement drunk tank—it’s more than a gimmick. With contemporary interiors by Alexandra Champalimaud, and a restaurant run by Lydia Shire, the Liberty is a good place for a weekend furlough. The clincher is the stone cruciform building itself, designed in the 1840’s by Gridley J. F. Bryant in the austere Boston Granite style. Until now, the only way to see inside this architectural marvel was to get yourself arrested—and that would have been significantly cheaper.