This is a fascinating and educational experience. It is the home of the largest cattle auction in the world. I attended on a Monday, the day the auction starts each week. Cattle is sold continuously until all cattle is sold and goes on through the night, usually lasting through Tuesday.
Throughout the stockyards, there is a cat walk which allows you to walk above the cattle to the stadium where the actual product is sold. Below you are thousands of cattle in pens, and you can watch as the workers sort the cattle by type. Further on down, you can watch as the cattle is identified and weighed for the actual auction. While I was there, they were selling 7,500 cattle. I was told that in the spring they usually have about 20,000 cattle there.
Inside the stadium, you can watch the actual auctioning. They move and sell these cattle so quickly, it was hard to identify who was actually bidding. (I guess these guys don't raise their hands.) And, of course, you have no idea what the auctioneer is saying!
If you go into the adjacent office building, you can get a book on the history of the Stockyards and a brochure on Stockyards City. This city has many neat shops which offer apparel, equipment, supplies, and dining.
The Stockyards are free of charge, and, although some say that tours are available, I couldn't find them. But it's quite easy to get around on your own. Boots are not necessary as you walk above the cattle. Just be prepared for a distinct smell and an overwhelming roar of the "moo" sound.