We've had so much fun hiking around Acadia - we put together a bunch or recommendations for different levels! We also highly recommend AllTrails if you want to look at allllllll the options!
Maine is so gorgeous and Mount Desert Island is just a teensy part of it! If you'll be staying more than just the weekend or if you're roadtripping to and from Bar Harbor, you might want to check out some of the other beautiful spots in the state!
Acadia is great for hiking, biking, and boating (both fresh and saltwater!). There are tons of different guided tours you can book and also plenty of places that rent bikes and kayaks for you to take out on your own!
Great for a rainy day or if you've had your fill of all the outdoor activities :)