WHERE IS THE BEST PLACE TO SPOT A BEAVER IN ACADIA NATIONAL PARK?

About 15 to 20 years ago you would not have had any problems spotting beaver in the park, that was before the park service began rounding them up and removing them from the park.  It is my understanding that the park service no longer does that, and that only distructive beavers are removed.  Sadly the damage has already been done and beaver sightings are way down.
The waters over by Duck Brook Bridge still have a few active beaver, the waters right behind that small building before the bridge.  You can see the nice beaver lodge out in the water.
One half of the Duck Brook Bridge Road is now closed to cars so to reach the area of the bridge by car you need to drive out  on the Eagle Lake road, route 233, and look for The Duck Brook Bridge road on the right..

WHY IS THERE A HELICOPTER AT THE BAR HARBOR BALL FIELD?

Nearly once a day throughout the Summer and Fall a lifeflight helicopter is called to the island - usually because someone has had a bad fall on a mountain in Acadia National Park or had a bad bike accident.  The Bar Harbor ball fields, the one closest to Main Street, is the landing zone for the helicopter.
If you are in downtown Bar Harbor and hear or see a low flying helicopter passing overhead, it most likely is Lifeflight either heading to the Ball fields or leaving the Ball Fields.

ARE THERE CAVES IN ACADIA NATIONAL PARK?

Yes, the mountain sides have a number of caves in various sizes, some are old bear caves while larger caves were once used by Native Americans.  Perhaps the most famous of these caves is called the Great Cave, a cave located along an abandoned loop off of the Precipice trail.  It has an opening that is 100 feet high and the cave goes back into the mountain side about 100 feet.  Even though it has been abandoned by the Park Service, a number of sites on line tell how to reach The Great Cave.
The second most famous cave in the park is yet another abandoned cave, Anemone Cave, an ancient sea cave that can only be entered at low tide.  People have become trapped and drowned in this sea cave so pay close attention to the tide.
The Bear's Den is an abandoned bear cave within sight of the Park Loop Road and hundreds pass it every day without ever knowing its even there.
There are many other caves you can find on line, including the caves of Day Mountain.

WHERE CAN I GO TO LISTEN TO LOONS IN ACADIA NATIONAL PARK?

Next to Whales, Loons produce the most beautiful sound, and can be found on many of the lakes and ponds in Acadia National Park.  To listen to Loons, the best time is at dusk, but you will want to bring along some good insect repellent as the bugs at dusk can be thick.
My favorite place to listen to Loons over the years has been at Bubble Pond.  Just find a nice spot along the shore and wait.

HOW CAN I GET INTO THE NATIONAL PARKS FOR FREE?

If you are disabled or a senior citizen, you qualify for a free lifetime pass into any of the National Parks.  And the free pass does not only cover you, it covers all the people entering the parks with you, as long as the pass holder is in the car - you don't even have to be the driver.
But the lifetime free pass goes even further - it entitles the pass holder to stay at any National Park campground for half price.  You apply for your lifetime pass by visiting any of the National Park headquarters.  They will give you a short form to fill out and ask to see two pieces of paperwork showing you are either a senior citizen or disabled, that's it, they give you your free pass right than and there.
These free passes have been available for a very long time but the Park Service keeps it low on their radar and most people don't even know about them.

HOW DO I GET TO BLACKWOODS CAMPGROUND USING THE FREE ISLAND EXPLORER BUSES?

At the Bar Harbor Village Green, get onto the Sand Beach bus.  It's last stop before turning around and heading back to Bar Harbor is at the Blackwoods Campground.

WHERE IS LITTLE HUNTERS BEACH?

Little Hunters Beach is a very small stone beach that is not marked and hard to locate if you are not from the area.  It is most famous for its perfectly smooth round and oval stones, which some believe hold mystical healing powers.  It is the only beach of its kind in Acadia National Park and is unmarked because the park service would rather people don't find it.
Since it is unmarked, I will give the easiest way you can locate this tiny stone beach.  Drive to Blackwoods Campground and park, or take the Sand Beach free bus from the Bar Harbor Village Green and get off at Blackwoods campground.  The campground road to the far left of the bus stop will take you to a service road,  which runs through the woods a short ways.  The service road comes out onto the One Way section of the Park Loop Road. 
Follow the road moving in the same direction as the traffic, and continue on until you come to a small bridge with a wooden stairway on the left hand side of the road.  That is Little Hunter's Beach.
Oh, and removing those perfectly shaped stones is illegal.