Three days is a good length for a first visit to Nantucket: enough to see the town, explore the island by bike and still have time to sit on a beach. This itinerary assumes you stay in or near Nantucket Town and use bikes, shuttles and the occasional taxi. Adjust for the season, since hours in winter and shoulder months are shorter.
Day 1: The town and its history
Arrive on a morning ferry and drop your bags at your inn. Walk up cobbled Main Street, admiring the brick sidewalks and the grand houses built with whaling fortunes. Visit the Nantucket Whaling Museum on Broad Street, where you can spend about two hours learning about the whale fishery, scrimshaw and the island's Quaker merchants. Have lunch in town, then take a tour. A guided historical tour gives context, while a self-guided audio walk lets you go at your own pace. In the late afternoon, stroll to Brant Point Light, then to Children's Beach. Dinner in town finishes the day.
Day 2: Beaches and the south shore
Rent bikes in the morning and ride the path to Surfside Beach, about three miles from town. Swim or walk the long south-shore sands, bringing a picnic and plenty of water. In the afternoon, continue to Cisco Brewers for a drink and live music if it is the season, or detour through the moors for views. Return to town by the bike path, with time for a rest and dinner. If you prefer calm water, spend the day at Jetties Beach, which is closer to town and good for children.
Day 3: Siasconset and the east
Pick a clear day for the ride to Siasconset, about seven miles each way along the Milestone Road path. Walk the lanes of the village, admire the rose-covered cottages and follow the Bluff Walk to see Sankaty Head Light from the nearby public roads. If you have energy, visit the Shipwreck and Lifesaving Museum on the way back or take the Polpis Road path through the moors. Alternatively, take the shuttle one way to save your legs. End the day with a sunset at Madaket if you have time, or a quiet dinner by the harbor.
Optional extras
If you have a fourth half-day, try a guided natural-history tour of the Coskata-Coatue refuge to reach Great Point Light, or hike the trails at Sanford Farm and Ram Pasture. Star nights at the Maria Mitchell Association's observatory in season are another memorable evening. Rainy day alternatives include the Atheneum, the Whaling Museum if you have not been, and browsing the shops and galleries in town.
If you only have two days
Combine Day 1 with the south-shore beach from Day 2, and ride to Siasconset on the morning of your departure if the ferry is in the afternoon. Skip the museums that are not essential and focus on the Whaling Museum and the cobblestones. If you only have one day, do the town and Brant Point, then a late afternoon swim at Jetties.
Practical notes
Book your ferry, accommodation and bike rental early. Download audio tours and maps before you go. Pack layers, sunscreen and a windbreaker. Reserve dinner in July and August. In the off-season, check which museums and restaurants are open, and plan around daylight, since sunset comes early. Respect conservation areas and stay on marked paths.
Pacing
Nantucket is a place for slow travel. Leave gaps in your itinerary for unplanned stops, such as a farm stand, a gallery or a bench by the harbor. If the weather turns, swap days and enjoy the indoor attractions first. The best three days on the island are usually those with a clear plan and plenty of room to wander.
Eating along the way
Plan lunches around your location: a sandwich or lobster roll in town on Day 1, a beach picnic on Day 2 and a bakery or market stop in Siasconset on Day 3. Dinner reservations are wise in summer. In the colder months, look for places that stay open through the winter, and keep in mind that bay scallops are a local seasonal specialty.
Rain plan
If the weather turns wet, swap outdoor activities for the Whaling Museum, the Atheneum, the Maria Mitchell Association's museums if they are open and a long lunch. Self-guided audio tours can be done in light rain with a jacket, and the shops and galleries of Main Street are a good refuge. Fog can clear by afternoon, so be flexible and check the forecast each morning.