I am from Maine, and August is a GREAT month to visit the coast. You need to spend a day walking around my old home town of Camden, Maine. You will NOT be disappointed. Walk the harbor, see the Schooners. Drive Route 1 from Portland / Freeport all the way north to Lincolnville Beach: every town along that path is just lovely. It's a 3 hour drive, and your eyes and mind will be stimulated by coastal town and village beauty.
Maybe you will be there for the lobster festival in Rockland Maine or the Blueberry festival in Union, Maine.
Acadia National Park is awesome: Thunder Hole is a must see.
Freeport, Maine is lovely to walk the down town: LL Bean factory store is amazing and worth checking out.
You can take the Islesboro ferry out of Rockland and drive around that island for the day in your car. Stop at a roadside deli for a sandwich.
SO much to do. Enjoy!