Vintage 70s Open Side Cutout and Back Swimsuit from Danswell by GiJu - made in Italy
Light as air stretchy sheer material - your bum will be visible, I have darkened photo of back for modesty. 77% nylon, 23% lynel spandex. There is very mild deterioration of the nylon, a bit of powder residue but the suit and its elastic seem to be holding up great. Gentle hand wash, and I would say avoid sitting on sand or rough surfaces.
Vintage S fits like modern S- 12. 5" across fullest part of seat, stretches to 17" so 32-34" hips. Bust approx 32-34". Waist approx 26-28". Approx 23" long not including straps. Each leg hole is 14" around stretching to 24". Quite adjustable and stretchy, model is 5'1" with 31" bust/34" hips and this was just a touch loose, probably due to model's short height.
Flaws: as noted the material has some deterioration which is likely to continue so wear with care, great for photo shoots and sitting in the sun.

This item is sold from an excellent, highly rated vintage boutique.