I just came back from Bar Harbor and riding in Acadia National Park. I was concerned that our Bike Friday's would not work on the gravel carriage trails. Well, they did. You don't need a mountain pike to ride these roads. The surface is smooth packed dirt with small gravel embedded in it - no loose gravel, no ruts. I rode a little slower than on a paved road, but had no problem, no slippage at all. So, if you bring your bike, you won't need to rent a mountain bike. You could spend that rental money on a bike rack......