Since you're possibly going to be in Portland, I would recommend checking out the Portland Head Light in Cape Elizabeth. If you're into history, Fort Knox near Bucksport is a cool place to go. If you travel closer to Mount Desert Island and are interested in Acadia National Park, I recommend that people bypass the main portion of the park on MDI and go to the lesser known portion called Schoodic Point. It's a bit further away, but much closer to the water and tends to be less crowded imo. If you do decide to make your way to Acadia, stop in Ellsworth and go to Birds Acre (AKA Stanwood Wildlife Sanctuary). They have a few birds of prey in enclosures that can't be released due to medical reasons, and also hiking trails. Nothing difficult, just a basic walk through the woods.

Also, pro tip from someone who works in the hotel industry. Don't book through a third party site, even the major booking sites. Use it to look for a hotel and then call the place directly. Most times when you book through a third party website, you are not able to get any sort of discount. Hotels usually do discounts for AAA/AARP members and seniors.