Turns out, Caitlyn Jenner's a big baseball fan -- or a big Kevin Costner fan -- 'cause she hit up the legendary "Field of Dreams" ball park in Iowa the other day ... and TMZ Sports has the pics.
We've confirmed ... Jenner stopped by the park on Saturday with a bunch of her friends ... before she took the stage on Tuesday for an event at her alma mater Graceland University in Lamoni, IA.
Our sources tell us the gang took a self-guided tour of the field -- and though stadium staff allows people to play catch on the infield, Jenner's group didn't do it.
And shocker -- we're told Jenner had a camera guy with her to document the entire thing.
"If you film it ... "