There are all kinds of things to do in Acadia! Hiking and biking are some of the most popular options. There are mountains, beaches, and lighthouses. Park Loop Road, provides a scenic drive where you can see Sand Beach and Thunder Hole among some other iconic landmarks in the park.
This is the highest mountain on the eastern U.S. seaboard and provides amazing views of the sunrise. In the winter it is actually the first place in the US that you can see the sunrise. If you want to do this you will have to get a pass, I have linked a website where you can go about that, but I do recommend getting on this early if you are interested, they sell out quick!! Also a note from my parents who have done this, dress warmer than you think you'll need to, take a blanket, and be prepared for a crowd!