Seguin is a must if you like lighthouses. There are caretakers in residence who will let you go up into the lighthouse. The island is high, so you get incredible views. Nice walking trails all over the island, too, and high cliffs where you can look down and see seagulls flying below you. . . .
There are three moorings in a small harbor. A bit crowded with local powerboaters on weekends, so arrive M-F and you should be good.
Edit: No anchoring
is allowed in the harbor, due to a power cable that runs there.