I had one of the best grade school trips of my life going to Mammoth Cave in fourth grade. And yes, I've been several times since, but this is one opportunity for families wanting to visit a national park they cannot pass up. 

On Saturday, April 21st, Mammoth Cave National Park will offer a fee free day for its visitors. The park will be offering free Discovery Tours.

It's a self-guided 3/4 mile tour beginning at the entrance of park's historic entrance. The tours will run from 10:00 a.m. until 3:00 p.m. CDT. While the tours are free, visitors may need to pick up tickets at the visitor ticket office.