Yesterday's high-octane excitement was a hard act to follow, so we decided to go underground today and just chill.  With a high temp of 95° in the forecast, Mammoth Cave National Park's cool subterranean hiking trails promised relief from the oppressive heat.
     
We opted for the two-hour/two-mile guided Historic Tour with a 300-ft elevation change.  As soon as we were within 100 feet of the cave entrance, we could feel the cool air reaching out to beckon us below.  Once inside we were treated to natural air conditioning that provided a welcome respite from the day's oven-like conditions.
     
As its name suggests, Mammoth Cave in central Kentucky is the largest known cave system in the world with more than 390 miles of explored cave passageways, all carved over the last ten million years by the what is now called the Green River.  After winding our way through the cave's dimly lit passages, including the tight squeeze at Fat Man's Misery, and down and up more than 400 stairs, we emerged back into the light (and heat) of day.  Having seen this amazing phenomenon, which has been designated a World Heritage Site, we had to hike the short trail down to pay homage to the river that had created this massive system of caverns.  The river was attractive—and green—but it certainly did not look as powerful as we expected it would.
     
Although Mammoth Cave was formed long before the United States came into being, the national park concept was conceived in the U.S.  While the concept of setting aside land for wilderness preservation had been discussed previously, the United States established the first national park for this purpose, Yellowstone National Park, in 1872. 
     
Steven had experienced other national parks when he visited California with his family a few years ago so this wasn't his first NPS experience.  Today he began documenting his visits by carrying his own National Park Service passport.
     

He's got a passport, and he knows how to use it.

After leaving Mammoth Cave, we headed north toward Louisville.  To give that passport a little more use, we stopped at the Abraham Lincoln Birthplace National Historical Park in Hodgenville, KY.  As soon as we entered, Steven headed to the passport stamps.  One of the park rangers saw him and recruited him to join the Junior Ranger program.  He dived into the requisite task immediately, tracking down information about the Lincoln family in the exhibits.  With less than an hour before closing time, he knew haste was essential.  The rangers were amazed when he returned so quickly with his activity book completed.  They checked his work and administered the Junior Ranger oath, in which he promised to explore, learn about, and protect the Lincoln Birthplace park.
     

Lincoln Birthplace's Junior Ranger Steven and Ranger Menge

Once that was done, we had just a few minutes left to visit the cabin.  Steven was understandably confused when we left the visitor center and followed the signs pointing to the cabin representative of the Lincoln birthplace.  He made no pretense of being knowledgeable about architecture, but he was clearly having a difficult time with what he was seeing.
     

"That's supposed to be a cabin?"

Of course, when we entered the memorial building, he saw the cabin that is preserved inside.  A flurry of controversy about the cabin's origin arose in the early twentieth century but was never resolved.  Finally in 2004, technology was available to determine that the cabin is definitely 39 years too young to be Lincoln's birthplace. 
     

The "Lincoln Birthplace" representative cabin

Since the cabin was from the area and close to the era, the park service maintains it so visitors can view a cabin similar to the one in which the 16th president was born at this spot in 1809.  Having visited the heart of the memorial, we had just enough time left to slip a few yards down a trail and log into a letterbox at the park.  Then we were off to Louisville, where we'll check out another product made in the USA tomorrow.