Tiring! LOL

Lots of walking and going up and down stairs in an above average carbon dioxide atmosphere combined to tire everyone out. I would recommend factoring that into planning a visit. I would leave a couple of hours of light activity between tours, if possible, for some recovery time.

I did not have any trouble with being underground in a confined space. These areas are generally as large as a typical room/corridor or larger. It is like you are in a house made from rough-hewn rocks. There were a couple of places where we were quite tight going through openings, and one short stretch where we had to bend over to walk, but generally it was not bad at all. Darkness was not an issue with the lighting, but when they turn off the lights in the second dome it gets DARK! (In case of total electrical failure, the rangers have flashlights plus there are various equipment stashes including lanterns in the cave.)

If you are inquiring as to how I found out about the cave tours, there is a thriving cave tour business in the USA. Pretty much all of the Mississippi River watershed was an inland ocean for many millions of years. When the ocean retreated, the limestone started to erode and corrode to form caves like Mammoth Cave. Starting around the late 1800s, people started offering cave tours. There are hundreds of caves open for tours over here. I literally grew up taking cave tours on a fairly regular basis.

For Mammoth Cave specifically, i go by it annually on my way to Mephit Furmeet. They have a full listing of current tours (and there are many!) on-line as well as at the Visitor Centers in the interstate road rest stops in the area, so I was able to get plenty of information and plan things out well in advance.

Some useful web sites:
Mammoth Cave National Park - https://www.nps.gov/maca/index.htm
Cave tours - https://www.nps.gov/maca/planyourvisit/gocavetours.htm (link for current season about halfway down the page)