This is me and Connor's favorite bar to visit when we're in NH. They have the best cocktails and we usually stop here for some oysters and a drink or two. The food is great and their brunch menu is to die for. Quick stop with cool vibes.
Making it's comeback after the State Street fire, Louie's is a great place to grab dinner if you're enjoying a longer stay. Chef Jeremy is the best in Portsmouth. It's also right near Street which is one of my favorite lunch places feat. street food from around the world.
Check out the harbor - I always recommend the Portsmouth harbor tours to visitors they're super fun, you'll see some seals. There's also clippers and other options but definitely walk around Prescott or behind Bow st and check out all the ships.
If you're spending a longer time in the area and want to do some leaf peeping head up to Northern New Hampshire on The Kancamagus Highway. Conway or Franconia would make an epic day trip for the guests who don't mind a drive (midwesterners) and would allow you to see the best foliage New England has to offer. This is close to where I went to camp and nearby where me and Connor used to have our fateful ski trips with Kerry - one of my favorite parts of the state.