Planalto has 2 buses every day to Porto Alegre (8hrs) leaving at 12:15 and 23:00. There is also a bus to Florianopolis on Sunday at 13:30.
Planalto bus station is on the corner of Venezuela and Chile.
Seven kilometer west of town is the beautiful Fuerte San Miguel an old Spanish fortress. There are infrequent buses going, but hitchhiking is also an option. If you have to wait for your connection it's worth a visit.