S.I. Swimsuit Model -- Rock Climbing In a Thong ... For Insane Shoot

It ain't just standing around and smiling ... the super hot models in the Sports Illustrated: Swimsuit Edition had to bust their perfectly sculpted asses for those iconic shots ... and we've got footage of the women in action.

The rock climbing ... the sand storms ... the punishing waves ... it was all captured by "SI: The Making of Swimsuit 2015" ... a 5-part series that will air this weekend on Travel Channel.

It's pretty crazy stuff -- you see all of the challenges that smokin' hot models like Gigi Hadid, Hannah Davis and the rest of the crew had to overcome to get those perfect shots.

Plus, have you ever seen a model rock climb in a thong bikini before?