Horse Pens 40 is a privately owned outdoor nature park located in St. Clair County near Steele, Alabama. The park is situated atop Alabama's third-highest mountain, Chandler Mountain, in the foothills of The Appalachian Mountains. The park is known among the rock climbing community as a premier bouldering site in the American Southeast. The site is also home to a "Bluegrass Park" where it hosts festivals showcasing the genre several time per year. The biggest of these festivals occurs on the Fourth of July. The park features both RV and primitive camping.

The park is recognized by the Alabama State Legislature in House/Senate Joint Resolution 177 as "The Home of the South's Bluegrass Music". The park got its name from the original deed; which when allocating the area of the plot stated "the home 40, the farming 40, and the horse pens 40"; each tract containing 40 acres of land.
Each year, the park hosts a leg of the "Triple Crown" bouldering competition.