The ferry docks are right at the center of town. Brant Point Light and Old Brant Point are about a 15 minute walk from the ferry dock. You also pass right by Brant Point light on the starboard side as you enter the harbor. You should be able to get a few good pics as you go by.

Sankaty Head Light is on the other side of the island. You can forget walking there because it is too far. Your best bet would probably be by taxi.

Great Point is only accessible with a 4-wheel drive vehicle with a permit. Then you pay $20 or so a day to drive on to the beach and out to the light. It is absolutely beautiful out there and worth the $150 a day 4-wheel drive rental (might even be more now)to go out there.

If you are on somewhat of a limited budget, I would skip Great Point. Brant Point is close and free, as well as the Old Brant Point. Sankaty will cost you a cab ride, to and from. There are usually some "Island Tour" buses around to. Most of the roads you would ride a bike on are crowded with cars and the view isn't that great because the roads are not along the coast. They are more in the center of the island. Nantucket's richest residents own most of the property along the coast and there isn't that much access to the water from these roads.

There are plenty of great stores and restaurants in the center of town. Walk the docks and surrounding areas for some superb scenic beauty. In season there are some beautiful flowers and bushes you don't usually see in other areas.

Nantucket is a beautiful island but public access to some of it's beautiful areas is somewhat limited. Maybe the Island Tour Buses is the way to go but I would ask if they give you a few minutes at the lights to get off and take pictures.

Bob