One of the Maine coast's little treasures is Fort Edgecomb, a blockhouse on the Sheepscot River on Davis Island, not far off Route One, north of the Wiscasset bridge, has a beautiful view of the river on a high corner on the island. There is not much parking. When the blockhouse is open you can go in and upstairs. There are picnic tables, but no bathrooms that I remember. It's a fun little excursion that might take you 20 minutes to visit or an hour if you want to relax and eat a picnic.
I came upon this blog posting on the New England Historical Society Web site. It tells more about history of this little fort.
For a bit more: http://en.wikipedia.org/wiki/Fort_Edgecomb