Really anything outside of "town" isn't a tourist attraction. Namely the beaches. 'Sconset and Madaket beaches are two of the best (beach map here: http://1.usa.gov/ofZ1Yj ) If you're in town, there's a little sea kayak rental place (Washington Avenue, seanantucketkayak.com) that will get you away from the crowds and out to the barrier beaches very quickly. Or take a sunset sail with one of the charters on the wharf. I'd reccomend Cap'n Jim on the Endeavor (endeavorsailing.com).

outside of town experience the windblown dunes, moors and stunning beaches