The Albacore is one of my favorite local activities. My Papa used to take my cousins and I here all the time as kids. I took Phil to see it for the first time when he was in New Hampshire for PlaneSense training. It cost about 10 dollars and you can walk through the submarine.
Nubble Lighthouse is one of the most photographed lighthouses in the world! Definitely worth a visit if you're in to lighthouses
Walking around downtown Portsmouth is an awesome way to spend an afternoon! It's a small historical town with a lot of good places to eat and shop.