Visit the Schoodic Peninsula.
In main part of park, hike one way along the coastal road and take the shuttle back. Hike up Beech Mountain. Ride your bikes on the carriage roads.
Take as many boat trips as you can. Ones I've especially enjoyed: nature tours from Northeast Harbor and Southwest Harbor and taking the boat to Duck Harbor on Isle au Haut and then hiking back to the main island harbor to catch the late day boat back to the mainland. BTW: I'm the kind of person who gets seasick, but these are sheltered waters and I had no trouble.
Further afield: Cutler Coast has some pretty wild hiking. There are hiking trails on Monhegan Island.
On the Acadia National Park website, there are many downloadable brochures which will help you to plan. There's even a 206-page "Guide's Guide to Acadia."
Enjoy!
2006 Tiger CX 4x4, 8.1 L gas V-8, Allison 6-speed