Having seen this first in "Close Encounters of the Third Kind", it was strange to see it in person, decades later, but wholly outstanding. It's mind-blowing to ponder that "ground-level" used to be that high.
Worth the drive during our visit in the Rapid City, South Dakota area; about 1.5 hours iirc.
The walk around the base took us about 60 minutes at a decent pace; a sign says 45 minutes. Somewhat hilly in spots, but do it if you can, or as much as you can.
The entrance fee to the national park was $11 for our car (not per person). Restrooms in the parking area at the base. Obligatory tourist trap stores at the park entrance.
Drive slow through the prairie dog area.
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