If you are driving up from Portland a stop at the Pemaquid Light would be worthwhile. In Mt Desert Island, the Bass Harbor Head lighthouse is past Southwest Harbor. Obviously, spending a day in Acadia, Bar Harbor, and Mt Desert in general will be very worthwhile. Take a schooner trip out of Camden Harbor. You might see whales, and it is a lot of fun even if you don't.
If you want a longer excursion, consider going downeast. Canada will be open soon - if you get to Lubec (home of the famous West Quoddy Head Lighthouse) after August 9 you should be able to drive over to Campobello Island (bring your passport). This is a very scenic place, and at the far eastern end is the East Quoddy Head Lighthouse, a spectacular old light.
Here is my response to a similar query a few weeks ago:
Plan on spending at least a full day in Portland. In South Portland of course is the iconic Portland Head Lighthouse. (It is NOT the "Portland Headlight" - a "head" is the term for a spit of land jutting out into the ocean). A trip on the ferry out to Peaks Island is fun - you can get a round trip ticket that lets you ride along as the ferry stops at several islands, although I like to just do the round trip to Peaks Island and get a nice bowl of clam "chowdah" for lunch at one of several little restaurants a very short walk from the ferry landing.
Heading north on I-95, you will probably want to make the obligatory stop in Freeport to visit the iconic LL Bean store. They set the standard for all the others that followed. Great quality, exceptional service. Then at Brunswick you will want to head East on Route 1. Down on the Pemaquid Peninsula you will find the Pemaquid Point Light House - a stunning light house with sweeping granite which makes for even more stunning iconic photos! Wandering further East you will go through Wiscasset and other quintessential little towns. I would plan on spending the night in Camden. They may still have schooner day trips in September. This time of years the Gulf of Maine is visited by Right Whales, finback whales, and Minke whales. Moving on, driving down the peninsula to Castine may be worth the detour - it is a beautiful little village, home to the Maine Maritime Academy. Before you get to Ellsworth you will go through Bucksport. On the right side of Rt 1 you will see the "Giant Chicken Barn Antique store". It will probably still be open - I think they are open all year. Worth a visit - they have three floors of really good stuff! Finally you will arrive at Ellsworth and head down Rt 9 to Maine's gem: Acadia National Park. The Loop Road and the road up Cadillac Mountain do not require walking and will afford great viewpoints. Plan on a half day walking around "Bah Hahbah". You should spend several days there: the rocks and ocean look differently at different times of the day. There is a nice walk by the ocean starting behind the big inn. Plenty of places to eat seafood.
Sadly in September most of the roadside lobster shacks will be gone, and MacDonalds may no longer have lobster rolls. But you should be able to find restaurants open in most larger towns.
Searsport is home to some good antique shops - some may be open in September.
Past Bar Harbor (past Ellsworth on Rt 1) is a big stretch of barren road. If you blink you will miss the little towns of Hancock and Milbridge. If the trees are turning, take a detour on Highway 182 (the "Blacks Woods Road") just East of Ellsworth - a windy route through some very pretty hills often taken by the locals to avoid the tourist traffic of Route 1 in the summer, and sometimes taken just to avoid the repetitive drive on Route 1 if one must do it frequently.... Do watch out for the ghost of the girl in the red dress, especially if driving through this area at night... It is a remote and lonely stretch of road - I wouldn't drive it at night without plenty of gasoline and a good car. The pavement is generally good, though - no worse than most rural Maine roads in terms of frost heaves and potholes...
Make sure you fill up your gas tank in Ellsworth. After Ellsworth you enter "downeast Maine". The way Maine used to be - not very tarnished by tourism. The last significant hotel or motel will be in Machias. A good place to stay a few nights. My brother and his wife spent three nights at a little Inn in Lubec a few years ago and absolutely loved it - not sure if they are still open. A day trip to Jonesport (a quintessential lobster fishing village) and the beach at Roques Bluff State Park will be fun. Another day - take the Cutler Road loop road (highway 191) out of East Machias. Some miles (10 or so) past Cutler you will find a gravel road off to the right - this is the Bogs Brook Road. This is land owned by the Maine Coast Heritage Trust. You can drive straight South on this road (don't take the right turn) and it leads to a parking area. It is a very short walk to a very pretty gravel beach with rocky outcrops. Many times I (or my wife and I) was the only person there for hours. Continue on through bog land, past "Bailey's Mistake" - you will come to the Boot Cove Rd on the right. These roads are not particularly scenic at this point... but this takes you directly to the road in Lubec going to the West Quoddy Head Lighthouse - the iconic red-and-white striped lighthouse. This is a state park, and you can sit on benches overlooking the ocean below the cliffs and looking across the Bay of Fundy to Grand Manaan Island. This is one of the foggiest places on earth, so you may encounter fog, and a foghorn. When I practiced medicine in Lubec one of my patients was a member of the Coast guard and his duty assignment was as the lighthouse keeper of the West Quoddy Head Light - it was one of the last lighthouses in the US to be automated. I had friends who lived out near the lighthouse. A beautiful spot, but there would be days when they would be in pea soup fog and a mile away in town it would be sunny and beautiful. This also happens in Jonesport.
The nearby town of Lubec is quaint - walk around by the small pier and the old sardine packing house and depending upon the timing you may appreciate the currents caused by the massive tidal change which can be as much as 28 feet in this area. Have your passport and vaccination cards with you in case Canada is open. If so, you can drive across the bridge from Lubec to Campobello Island. Exploring Campobello could take the better part of a full day. There is a beautiful beach at Herring Cove. The Roosevelt Cottage (a "cottage" in New England generally refers not to size but to a house which is not insulated and winterized - this beautiful Victorian home is huge - and yet it is a "cottage") is worth a visit. Across from the cottage is a road worth taking - about a mile down on the right is a Public Access to a bog with a boardwalk around it. There are pitcher plants, sundews, and other interesting plants there.
At the far end of Campobello is the East Quoddy Head Lighthouse. A stunning lighthouse. At low tide you can walk out to the head and wander around the lighthouse - but the head is cut off by the incoming tide, so there is only two hours or so when you can walk over to it. The tide runs quickly across a sandbar, making traversing it impossible.
Even if you do not walk over to the lighthouse, the views from the parking area are spectacular - not only of the light but of the surrounding sea. You sometimes will see whales spouting from here.
Be aware that cell service may be spotty when you get past Ellsworth!
Heading back to Route 1 from Lubec, you can go to the Cobscook Bay State Park - this quiet bay is one of the most peaceful spots anywhere.
The fast way to get back to Portland would be to go on up to Calais (pronounced "Callus") and take Rt 9 to Bangor, then I-95 to Portland. Otherwise you can backtrack down Rt 1.
FYI: I mention several beaches. Beaches are significant in Maine, because with 3600 miles of coastline, only about 40 miles are considered "beach". And some beaches are gravel or rocky beaches. A "real" beach is so rare in Maine that at Acadia National Park they named the beach "Sand Beach". Which for most people would seem redundant... Of course, don't bother bringing your swim suit to the beaches in Maine. The reason Maine has not been more commercialized is that the water is very, very cold.
A few of my posts:
Mixed set: http://www.uglyhedgehog.com/t-146468-1.html