The famous train ride up the Serra do Mar back to Curitiba is a perfectly viable day trip in itself — go up by bus, descend by train, or vice versa.
Ilha do Mel is the standard escape. The car-free island lies just outside Paranaguá Bay; boats leave from a terminal a few minutes outside the centre. There are two settlements, both very small, two long beaches, and an 18th-century Portuguese lighthouse. Possible as a long day trip but better with a night.
Antonina, a smaller and arguably more atmospheric colonial town, is 40 km away on the bay and reachable by bus.
The Marumbi State Park, on the railway line back to Curitiba, has hiking trails up to peaks above the rainforest. You can board or alight at the small station mid-route — confirm with the train operator before booking.
