Trosa is a town in Södermanland County, with 5 000 citizens in the town itself, and 12,000 in total in Trosa municipality, Trosa kommun.
The other dominant settlement is Vagnhärad, at the Stockholm-Malmö rail line.
Trosa is a busy summer resort 60 kilometres south of Stockholm.
- Tullgarn Palace
- Tureholm Palace
Diving in Vagnhärad limestone quarry.