The 30-year-old wide receiver shared the view with all his Instagram followers on Friday ... posting a shot of him lying down on a yellow float in a swimming pool with two women chilling nearby.

Of course, goin' nekkid is a lot more common in Europe than in the States ...  so ya can't blame Stills for showin' off all his ass-ets with a hilarious smirk on his face.

Stills leaned into the hilarious moment ... dropping a 🍑 emoji in the caption instead of using words.

It's obvious Stills is enjoying the first week of summer -- besides skinny dipping, he also made an appearance at Louboutin's event in Paris and stopped by Duomo di Milano Cathedral in Italy.

The 9-year NFL vet is currently a free agent after his second stint with the Saints last season ... and has shown some interest in playing for the Tennessee Titans.