The 40-year-old host and 26-year-old actor go bare-chested as they descend a cliff in the Catskill Mountains to the water below. Grylls chose an area of the mountain range where special forces trained in the 1800s, and told People he thinks Efron "got to use his muscles to their max."
"We reached out to [Efron] and he kindly said he was a fan of the show and that he was in 120 percent," Grylls said. "He asked for the biggest, baddest adventure and it was an honor to oblige."
The new series is an unscripted reality show that sees Grylls take celebrities on 48-hour survival adventures in the wilderness. Each episode follows one celebrity's adventure, and future guests include Channing Tatum, Ben Stiller, NFL Hall of Famer Deion Sanders, actor Tom Arnold (True Lies) and Today host Tamron Hall.
"Running Wild allows viewers to see inside the hearts and minds of these guests in a very open, honest and vulnerable way, pushing them out of their comfort zones and seeing what they were like in real life when stripped of all the benefits of celebrity," Grylls detailed in June. "Ultimately, this show is about taking these stars on the adventure of a lifetime and being alongside them when they discover something new and empowering about themselves and their world. For me, that is always a privilege."
Efron's episode kicks off the series July 28 on NBC.