Leonie Hanne is adding a new stamp in her passport ... because she's on a getaway in Asia, and she's bringing the heat.

The German fashion model is visiting Thailand for an island adventure ... her vacation -- and her body -- looks like a dream.

Leonie is showing off the goods in some sexy bikinis ... busting out the swimwear for some boat rides and poolside relaxation.

All of Thailand's greatest hits are on display here ... monkeys, jungles, infinity pools, islands ... and Leonie's soaking it all while looking amazing.

Leonie's worked with huge brands like Dior, Cartier, Louis Vuitton, Givenchy and Tommy Hilfiger ... and she's making Yao Noi Island her own personal runway.

Slay!!!