Several lovely, paved bike paths radiate from the center of town to outlying beaches. The bike paths run about 6 1/4 miles west to Madaket, 3 1/2 miles south to Surfside, and 8 1/4 miles east to Siasconset. To avoid backtracking from Siasconset, continue north through the charming village and return on the Polpis Road bike path. Strong riders could do a whole circuit of the island in a day. Picnic benches and water fountains stand at strategic points along all the paths.
For a free map of the island's bike paths (it also lists Nantucket's bicycle rules), stop by Young's Bicycle Shop, at Steamboat Wharf (tel. 508/228-1151; www.youngsbicycleshop.com). It's definitely the best place for bike rentals, from basic three-speeds to high-tech suspension models. In operation since 1931 -- check out the vintage vehicles on display -- they also deliver to your door.
For shellfishing you'll need a permit from the marine coastal resources office at 34 Washington St. (tel. 508/228-7261), which costs $25 for nonresidents for the season. You'll see surf-casters all over the island ($10 permit required). Deep-sea charters heading out of Straight Wharf include Capt. Bob DeCosta's The Albacore (tel. 508/228-5074; www.albacorecharters.com), Capt. Josh Eldridge's Monomoy (tel. 508/228-6867; www.monomoychartersnantucket.com), and Capt. David Martin's Absolute (tel. 508/325-4000; www.absolutesportfishing.com). On the Absolute, a 5-hour bass-fishing trip for up to six people costs $1,100; for 2 1/2 hours, it is $550.
Nantucket Health Club, at 10 Young's Way (tel. 508/228-4750; www.nantuckethealthclub.com), offers all the usual equipment and classes. Nonmembers pay $25 a day.
Two pretty courses are open to the public: the 18-hole Miacomet Golf Course, 12 W. Miacomet Rd. (tel. 508/325-0333; www.miacometgolf.com), and the 9-hole Siasconset Golf Club, off Milestone Road (tel. 508/257-6596). You'll pay $125 for 18 holes at Miacomet. At Siasconset, playing 9 holes costs $35.
Through preservationist foresight, about one-third of Nantucket's 42 square miles are protected from development. Contact the Nantucket Conservation Foundation, at 118 Cliff Rd. (tel. 508/228-2884; www.nantucketconservation.com), for a map of its holdings ($4), which include the 205-acre Windswept Cranberry Bog (off Polpis Rd.), where bogs are interspersed amid hardwood forests; and a portion of the 1,100-acre Coskata-Coatue Wildlife Refuge, comprising the barrier beaches beyond Wauwinet. The Maria Mitchell Association sponsors guided birding and wildflower walks in season.
The town courts are located next to Jetties Beach, a short walk west of town; call the Nantucket Parks and Recreation Commission (tel. 508/325-5334) for information. The town courts cost $20 an hour for singles and $25 an hour for doubles. Though it's not generally open to the public, the grand, turn-of-the-19th-century Siasconset Casino, New Street, Siasconset (tel. 508/257-6585; www.siasconsetcasino.com), occasionally has courts available for rent for nonmembers from 1 to 3pm for $40 an hour.
Jetties Sailing Center manages the concession at Jetties Beach (tel. 508/228-5358), which offers lessons and rents out kayaks, sailboards, sailboats, and more. Rental rates for single kayaks are $20 to $25 per hour; sailboards $20 to $25 per hour; and Sunfish $35 per hour. Sea Nantucket, on tiny Francis Street Beach, off Washington Street (tel. 508/228-7499), also rents stand-up paddleboards and kayaks; it's a quick sprint across the harbor to beautiful Coatue. Single kayaks rent for $40, and tandems for $70, for 4 1/2 hours. Nantucket Island Community Sailing (tel. 508/228-6600; www.nantucketcommunitysailing.org) gives relatively low-cost private and group lessons from the Jetties pier for adults (16 and up) and children; a seasonal adult membership covering open-sail privileges costs $250 for 4 weeks. One 2-hour private lesson costs $125.
Gear for scuba-diving, fishing, and snorkeling is readily available at the souvenir shop Sunken Ship, on South Water and Broad streets, near Steamboat Wharf (tel. 508/228-9226; www.sunkenship.com). Snorkeling gear costs $20 per day, and scuba-diving gear costs $50 per day. A 2-week scuba-diving course is $550.