Usually I post a desert destination on Mondays, but this week I have a fascinating destination from the Midwest, where I recently visited.
One evening after cave rescue classes, I was able to get away to nearby Bluespring Caverns, a commercial cave with boat tours along the Myst'ry River.
[Image](Photo courtesy of Bluespring Caverns website)

Our after hours tour began with the owner, Jim Richards, giving us an orientation outside the visitor center/gift shop. 

[Image]Then we walked right under the building and down a steep path into a huge sinkhole, with tall trees rising all around us.
[Image]As soon as we got near the entrance, the temperature dropped from the 80s to the 50s. The interior cave temperature is about 52 degrees Fahrenheit. 
[Image]We could hear water before we see it, and we kept going down and down until we reached the river. Bluespring Caverns has the distinction of having over 21 miles of passage in it, including three miles of navigable cave stream passage, the longest in the U.S. We boarded a boat to begin our voyage.
[Image]My pictures don't do justice to what a magical trip it was. Once we left the dock, the only lights were those on the boat, so it was dark up ahead and dark behind us. We felt like explorers (with a really knowledgeable guide). At times we could see that  the water was only a few inches deep, while other times we didn't know how far the murky depths extended.
[Image]Much of the cave has been explored by cave divers, who have found numerous side passages, like the one shown above. We could even feel some air flow from this hole. The cave was found in the 1800s and we could only imagine what the earliest explorers thought as they went about with rudimentary gear.
[Image]Being an ecologist, one of my favorite things was looking for cave life. I saw some white crayfish and also cave-adapted Northern Cavefish (Photo above, courtesy of Bluespring Caverns website). The fish seemed to like hanging out near the walls of the cave.  
Not only were the sights marvelous, but also the sounds of the cave, the gentle movement of the boat, and the river's current as it moved through the cave, slowly eroding away the limestone rock to make larger passages.
The tour lasted about an hour, and then we got to take a peek at the overnight facilities. In the winter months, the caverns offers youth group camping, with a boat tour, a "wild" adventure tour, and then camping on bunkbeds in an upper part of the cave. It looked like it would be a lot of fun.
I would definitely recommend a trip to Bluespring Caverns--it kept me smiling the whole time and I can still picture myself cruising slowly on the underground river. For more information, take a look at the Bluespring Caverns website.