Portsmouth is one of my favorite places in NH, on that short bit of shoreline NH has.
The Strawbery Banke restoration is wonderful - done by the same man (or men) who
did the Williamsburg restoration. It's been years since I was there,
so it probably is even better if it hasn't gotten too
commercialized. Also John Paul Jones' home is in Portsmouth and
several good restaurants. The Blue Onion, right on the water is the
one I remember especially. Reservations required as there are only
two sittings. It was great food, prix fixe menu, china and crystal
(butunmatched). If you try it, I do hope it is still the same. It
had so much charm along with the excellent food. I remember a great
steakhouse (but not the name). It is likely all changed anyway, but
you are bound to like Portsmouth.