Several companies lead guided tours of Portsmouth Harbor, taking in the islands, lighthouses, and scenic waterfront. The most intimate is the Tug Alley Too (47 Bow St., 603/430-9556 or 800/884-2553, www.tugboatalley.com [1], May–Oct., $49 adults, $29 children under 12), a tugboat that once carried lobsters to islands on the Maine [2] coast. Now owners Bob and Natalie Hassold take her out for one-and-a-half-hour spins around the harbor, with a maximum of six passengers on board.
A cheaper but more crowded tour is offered by Portsmouth Harbor Cruises (64 Ceres St., Portsmouth, 603/436-8084, www.portsmouthharbor.com [3], $16 adults, $14 seniors, $11 children), with several different routes aboard the M/V Heritage.
You can get out on the water in decidedly smaller craft through Portsmouth Kayak Adventures (185 Wentworth Rd., Portsmouth, 603/559-1000, www.portsmouthkayak.com [4]), which leads guided trips around the Piscataqua River estuaries as well as out on the open ocean of Portsmouth Harbor. A two-and-a-half-hour trip is $59. Full-day rentals are available for the same price.
Links:
[1] http://www.tugboatalley.com
[2] http://www.moon.com/destinations/new-england/maine
[3] http://www.portsmouthharbor.com
[4] http://www.portsmouthkayak.com