As Woody Harrelson sat barefoot (“I’m more comfortable like this”) in a London hotel suite to chat about “War for the Planet of the Apes” (opening Friday), the actor smiled and clearly flashed back many years when asked his favorite Chicago memory.

Noting that “I haven’t been to Chicago in a long, long time,” Harrelson still recalled going to a “kind of therapist who did this thing where you regress back to your birth through a breathing technique. I had never done anything like that before — or since, for that matter.”

The therapist, whose name is long forgotten, kept him breathing intensely “for, like, two or two-and-a-half hours. … But for me, it seemed like it only lasted 10 minutes. It was one wild experience, but it happened in Chicago! It blew my mind!”

As for the Colonel J. Wesley McCullough he portrays in “War for the Planet of the Apes,” Harrelson disputed the description of his character as scary.

“I’m not playing a scary guy — from my point of view. He’s simply a guy who completely believes he’s doing the right thing. He believes it’s absolutely necessary to kill all the apes before they evolve into complete human-like intelligence — and the humans regress back to the level of the apes. For the colonel, it’s all about it being necessary to save humanity.”