Since it has been mentioned Portsmouth, NH is a cool town - good stop on the drive from Boston to Maine. Cute little downtown with a bunch of nice restaurants and shops.
Portsmouth is the home of Strawbery Banke, which is a great place to visit if you a history buff at all.
Second the recommendation for Bailey’s Island. I have friends who have a home there and it’s wonderful. It isn’t right near Portland, maybe about 45-60 minutes away.
Fun fact: Maine’s coastline is so jagged that it’s over 3,000 miles long! I didn’t believe it at first until I studied the map. There are lots of fingers of land jutting out into the ocean.
That’s why the saying in the state is “You can’t get there from here.” Often, it’s much quicker by boat than by land.
Love Peaks island for a quick day trip. Take bikes across on the ferry - bike around the entire island. You can stop several times to get over to the rocks and sit there for a while, taking in the gorgeous view. And there are lots of places just off the road where you can relax and enjoy a picnic lunch or a nap 
End with ice cream at the harbor and dinner back in Portland before heading home.
We’ll have to check out some of these other recommendations…
@doschicos, we learned when we first moved here that the Maine Gazetteer was a must-have! It even has our tiny camp road that forks off a remote logging road. It’s saved us quite a few times. We love exploring.
Has no one mentioned the Sunday Brunch at Harraseeket Inn, Freeport? All the Maine lobster you can eat ! A bit more upscale than alot of the restaurants in Freeport but we never miss brunch there.
^Never tried that, @NEPatsGirl. May have to request that on my birthday weekend in July.
@MaineLonghorn, be sure to make reservations, probably at least a week in advance. We’ve been lucky enough occasionally to walk in off the street (after being told they were full and not taking ressies).
@NEPatsGirl, thanks for the heads-up. We’ve learned after many years that we have to think about reservations during the summer. It still takes us by surprise - where do all these people come from? 
Can’t imagine why anyone new would avoid rt 1. Unless you’re coming through when Wiscasset is backed up, it is sooo worth it to drive the coast. So many water views.
Coming back down today (and I purposely went through Kennebunk and down through Ogunqiit,) the day was splendid.
I guess I’d only been to Kennebunkport before. I liked the former much. Chock full of old homes. Touristy, but right now, and in Sept, not bad.
There are so many cool places, if one is open to traveling Route 1
I’m beginning to think that @MaineLonghorn and I and some of the other Maine residents ought to be scheduling coffee or brunches or something with all of you who are passing through our area!
For that matter, we know each other’s kids, but not each other. And we even have friends in common, I think!
I am going to bookmark this thread since we love Portland! We enjoyed staying at The Press Hotel. It used to be the newspaper building and retains the theme.
If you like oysters, the Eventide is the place to go. Long wait but they have a good system for letting you know where you are in line via text and website. Central Provisions is also very good.
For beaches, two of the most beautiful in New England are Popham and Reid State Parks. They are near Brunswick and Bath respectively.
Yes, great beach recommendations, @lbowie. Both are actually closer to Bath. If you visit either beach, have lunch or dinner at Five Islands Lobster Company. Great seafood and a most spectacular setting. I recommend their fried scallops.
I need to save this thread for my October trip. We went to Old Orchard Beach and were surprised at all the French Canadians there.
We’re going to Portland for a wedding this weekend. All the guests are invited to the rehearsal dinner and wedding/reception, but I think I’m going to try and get to one of the oyster places mentioned above on Sunday before we drive back home.
Bath has a really nice old fashioned downtown. There’s a fantastic gourmet cooking shop called “Now You’re Cooking,” and of course, Reny’s. The Solo Bistro or Beale Street Barbecue are both excellent restaurants in Bath.
@NoVADad99 I used to work in Biddeford, just south or Old Orchard Beach. French was spoken on the streets there. I used to love the cookies at Reilly’s Bakery.