The Blue Hole aka The Gulf
The Gulf, which is known as "The Blue Hole" by locals, is in Wayne County, Missouri, not too far from Piedmont, the "UFH capitol of the world." This is not worth a long drive to visit, but if you are in the area, or visiting Clearwater Lake or Markham Springs, do take a side-trip to visit it, unless, that is, you just want an excuse for a long country drive through beautiful countryside.
From Piedmont Missouri, continue on and follow Highway 34/49 south for 7 miles. Continue on Highway 49 to the left (do not go straight onto 34). You will go two miles, through the small town of Leper, and then arrive at the small town of Mill Springs. At the stop sign in Mill Springs, turn right to continue on Highway 49. Travel about another 2 miles and turn right onto County Road 442 (also known as Carson Hill Cemetery Road). Travel 1.8 miles (you will pass County Road 444 that goes to the cemetery). If you cross a low water bridge, you have gone too far; turn around and come back. Turn right onto onto County Road 443b and go .3 miles and the parking area is on the right side of the road.
After parking, it is only a few feet to walk to the hole. The rim of the hole is 40 feet above the surface of the water below, so be careful when leaning over to look down. I leaned on a tree for support as I was a bit intimidated.
This is described as a sink hole or a collapsed cave which is submerged.
What you can't see is even larger than what you can see. A good read is the book Geologic Wonders and Curiosities of Missouri by Thomas R. Beveridge (second edition, 1990), page 198 and 199. (Note, the book is free to read on share.mo.gov - click on the above link; and it is also free on the internet archive and other places).
The Blue Hole opens into a cave that extends for another far beneath, with divers exploring the underground.
For the adventurous, a somewhat more difficult path leads down into the sinkhole and the edge of the water, but we did not go down as we are getting older and sometimes we just opt out, even though we could make it. Be careful not to fall in the water as it is better with a boat and caving gear.
