As night falls, the motels and R.V. parks along America’s highways begin to fill up with travelers needing a place for the night.

But to untold thousands of motorists each year — some with a sense of adventure, others looking to save a buck, still more with no other place to go — Walmart is often a willing host for overnight guests.

“It’s not pretty: no pine trees, no bubbling brook, no ocean beach,” Chuck Woodbury, the editor of RVTravel.com, said in a tutorial video intended for casual travelers. “The idea of staying at Walmart is to park for the night, to get some sleep and then move on.”

Walmart’s practice of letting people populate many of its parking lots has made the retail giant’s stores a reliable, if somewhat improvised, destination and a place where an informal culture emerges before and after dark.