"We did this bit when Shai had to be facing down and I had to be the other way, and it was a little daunting," James said of scaling the 80-foot concrete structure.
"I was facing the ground, walking backwards," Woodley explained. "I was holding onto Theo's shoulder like it was the last thing!"
In the sci-fi adventure flick, Beatrice Prior (Woodley) and Tobias Eaton (James) get past the wall enclosing Chicago and venture into the world outside, which they quickly learn is more dangerous than ever before. The duo must determine who they can trust as a ruthless battle erupts in their new environment, which threatens all of humanity.
Fellow co-star Miles Teller told ET he's doing all of his own stunts in the movie and even went to the shooting range to prepare for filming. Meanwhile, Ansel Elgort revealed that his action scenes might be too much for his wardrobe to handle.
"My whole costume got torn up yesterday," Elgort said. "This is a new one. By the end of today it'll get totally torn up."
The Divergent Series: Allegiant hits theaters March 18.