The Great Cave, lost for a century, has been discovered. I wasn't the first to find it, but I'll go ahead and be the first to tell you how to get there. But please, be respectful of this amazing place. Not many know it even exists but if you're reading this, I'm assuming you know about it and are searching for it. Remember, the trail is dangerous enough that the park pretends this natural wonder isn't there.
The trail begins at the Precipice parking lot shortly before the section of the park loop road you have to pay to visit where Sand Beach and Thunder Hole reside. The Precipice trail is closed every year until August 15th when the endangered peregrine falcons are done nesting on the cliffs. Follow the trail for a few tenths of a mile up to the steep rock slide. About a third of the way up the slide over some difficult boulders, the trails veers to the right and begins its ascent up the deadly (yes, people die here) part of the trail where iron rungs and ladders are needed. Rather than follow the trail, go straight, straight up that rock slide. If you are not an experienced hiker I do not recommend doing this, it is extremely intimidating and humbling standing in the middle of a rock slide beneath enormous cliffs known for claiming lives.
Honestly it's slightly easier once you leave the trail as the boulders get a little smaller, however, the mountain gets steeper. Aim for the break in the trees above the slide, this is where the old trail went, its remains can still be seen today. Once leaving the open rock slide, you'll enter the treacherous woods above it. It continues to get steeper, but this time there is only dirt and crumbling rocks at your feet with an occasional tree or branch to grab hold of. This type of terrain is extremely slow going, especially on your way back down. But once you hit the trees, you're almost there. (A father and his two sons saw my wife and I descending and assumed it was the trail, they were instead treated to a surprise visit to a lost cave but were so scared at this part of the 'trail' they almost turned back. They didn't, they made it.)
Follow the remnants of the trail, at one point you actually ascend some century old stone steps placed there by famed trail maker Rudolph Brunnow long ago. You can clearly see the granite stairs starting in the lower right hand corner of the picture to assist you up the steep slope. Through the thin birch forest you can make out a dark spot in the massive rock wall, that's the Great Cave. The trees now block most of the view but I bet at one point you could get a clear shot of the ocean from the mouth of the cave.
Standing at the foot of it is awe inspiring. It's not the 100 foot by 100 foot entrance described in old trail guides but believe me when I tell you pictures do it NO justice. Due to the color of the granite it's hard to distinguish the depth in photographs, seeing it with your own eyes is a sight to behold. There is a giant boulder lodged in the mouth of the cave hanging a good fifteen feet above you (but look closer and you'll realize its not a hanging boulder but actually a land bridge connecting the two massive rock ledges). The moss covered walls climb up to a crumbling ceiling that stays damp at all times, coated with moss and tiny ferns. The deepest part of the cave is dark (a flashlight isn't necessary) and most likely never sees even a minute of sunlight. I unfortunately didn't bring a tape measure but it must be close to fifty feet deep, maybe twelve feet wide at its widest, progressively getting tighter the further in you travel. I've been to some truly amazing places, this one is unlike any of them. It should have never been forgotten, but I suppose that makes it more special for those who find it.
https://www.amazon.com/Acadia-You-Havent-Seen-Abandoned-ebook/dp/B074N92TN9/ref=sr_1_1?ie=UTF8&qid=1505787301&sr=8-1&keywords=the+acadia+you+haven%27t+seen[A year later I returned with more knowledge on the subject and realized there is actually another easier trail leading to the cave as well as a trail leading away from it and back towards The Precipice path. This new information is in my book "The Acadia You Haven't Seen" along with over FIFTY other hidden and forgotten sites throughout the island.]