The identity of National Park Mystery Spot 25 is hidden in these clues. Were you able to figure it out?
A trunk in a shell serves them well.
The hexagon held them against their will.
No lake, no pond, no bog; not even a puddle to wet a frog.
Seven in a cluster is the land it can muster.
Bonus clue, no extra charge: 'Tween your toes it will ooze, and it clings to your shoes.
The answer is Fort Jefferson in Florida's Dry Tortugas National Park. Congratulations to Eric, who was the first to supply the correct answer (at 6:41 am EDT). Eight others also ID-ed this mystery spot: Anon (7:35), Ed123, L Bebout, Davey J, y_p_w, Steve B, RangerLady, and Road Ranger. Good job.
Here is how the clues take you to the answer:
A turtle has a shell of bony or cartilaginous material (actually formed from ribs) that encloses and shields its trunk. Thus, where turtles are concerned, "a trunk in a shell serves them well." The Spanish term for turtles is tortugas. The Spanish gave the name Dry Tortugas to a group of islands situated in the Gulf of Mexico at the end of the Florida Keys about 70 miles west of Key West, Florida. The name derives from the abundance of sea turtles that Spanish explorer Ponce de León saw when he visited the islands.
The Dry Tortugas are indeed very dry. None of the islands has fresh water on its surface. Thus: "No lake, no pond, no bog; not even a puddle to wet a frog."
As the name implies, Dry Tortugas National Park is located in the Dry Tortugas. The park encompasses 101 square miles (64,701 acres), 99.9% of which is water covered. The land area, just 39 acres, exists in the form of a cluster of seven small islands. Thus, for this particular park, "seven in a cluster is the land it can muster."
The centerpiece attraction of Dry Tortugas National Park is Fort Jefferson, a hexagon-shaped brick masonry fort constructed (though not quite completed) on Garden Key during a nearly three-decade period beginning in 1846. Although Fort Jefferson was never attacked, it famously served as a federal prison until 1874. The convicts incarcerated at the fort -- mostly Army privates convicted of desertion and civilians convicted of robbery -- shared a condition in common: "The hexagon held them against their will."
The bonus clue " 'Tween your toes it will ooze, and it clings to your shoes" refers to mud. Dr. Samuel Mudd, a physician who was sentenced to life in prison for aiding Lincoln assassin John Wilkes Booth, was famously imprisoned at Fort Jefferson until he received a presidential pardon in March 1869.
Postscript: The park originated as Fort Jefferson National Monument (via presidential proclamation on January 4, 1935) and bore that name for the better part of six decades. It was redesignated Dry Tortugas National Park on October 26, 1992.