If you're planning on staying there over the weekend, there's a lot of things to do in Maine.
Places I went to:
Sight-seeing: Portland Head Light, Bug Light, Portland Art Museum (it was free on Friday Evening), Portland Observatory, Back Cove/ Eastern Promenade Trails, Downtown/ Old Port, DeLorme Map Store (if going to see a giant globe of Earth is your kind of thing to do lol, it's also far away).
Food: Fisherman's Grill, Duckfat, Bite into Maine, Gorgeous Gelato (hilarious owner xD), 3Buoy's Seafood Shanty & Grille, and Street & Co.
If you need rental car, make sure you get free pickup/ drop off. I used Enterprise and they were very nice.. weekend special for $72/4 days and gave me a free upgrade to a better car. I stayed at Super 8 and their service was great. They let me use their refrigerator and microwave.. overall very friendly service from every place I went to.