The guides at Free Tours by Foot offer their expertise to visitors on free group tours for a simple reason: they love to share their city's history and quirks with others—and if they get a tip from thoroughly entertained tour-goers, all the better. They've curated a handful of tours for about nine cities, including a roundup of public art in New York City's subway system, a colonial jaunt featuring Revolutionary War sites in Boston, and visits to architectural feats in Chicago's Loop and the hospital where the first Chicago-style hot dog was born. Tour guides can also be commissioned for private, fixed-price tours of the same spots.