Portsmouth, New Hampshire is a compact, walkable coastal city with historic seaport charm, a lively arts and dining scene, waterfront parks and easy outdoor options (beaches, kayaking, nearby trails), so several-week assignments feel like an active mini-residency rather than being stuck in a dull place.
For bigger-city variety, Portland, ME (~50 miles) and Boston (~60 miles) are close enough for weekend cultural outings, airports and expanded nightlife.