Anitta Strips Down to Bra, Spandex Shorts During Snowy Mountain Vacation

Anitta's saying hello to the New Year by waving goodbye to clothes ... stripping down to a bra and underwear while hanging out in snowy Switzerland!

The singer-songwriter posted about her icy vacay Thursday morning ... sharing pics where she's lounging on a chair in the middle of the snow -- wearing the bra, underwear, a beanie and heavy boots.

She's playful in these shots ... tongue sticking out and a big smile for the camera while perched on the windowsill of the cabin where she stayed with her pals.

If you can believe it, Anitta ended up wearing even less before the trip was done ... going all the way down to a towel and nothing else for a sauna session with one of her pals.

To be fair, the Brazilian star did end up wearing more clothes when she got farther away from the abode ... sharing pics in chic snowsuits and thick sweaters on top of the snaps of her scantily-clad bod.

Anitta captioned the post, "No filter! Just pure happiness with @airbnb giving us the best trip of our lives 😍" -- so, clearly the rental giant helped her out on this trip.

Tons of celebs enjoy a good beanie, BTW ... so check out all the pics of celebs wearing their hottest headgear.