Marathon Sports has four locations: Cambridge, Boston, Wellesley, and Brookline. The store is completely geared around runners. It carries light racing shoes, cross trainers, and hard-to-find stabilizing shoes. The staff is trained to watch customers walk and jog to suggest different model sneakers. Whether you accept their advice or not, the personal attention and outstanding inventory makes this a great place to for serious runners. Store hours vary, but most are open 10:30AM to 6 or 7 PM. The website is really helpful, so check your location's hours if you are trying to head there after work. You may be cutting it close.