The historic centre is entirely walkable. It is roughly 15 minutes across at its widest point, and the river loop that defines the old town means most of the sights are within a few minutes of each other on foot. Cars are not permitted in the historic core, which makes the streets unusually quiet and pleasant to walk.
On foot is the only way to see the old town properly. The lanes are too narrow for bikes in places and most of the interesting spots are on pedestrian-only streets.
By kayak or raft, the river provides a different angle on the town. Rental operators near the river offer hourly hire; floating the loop around the old town takes an hour or two and is one of the best ways to spend a summer afternoon.
By bicycle for the surrounding countryside. Bike rental is available in town, and the cycling routes through the Šumava foothills and along the river valley are good. The terrain around the town itself is hilly, so expect some effort.
For transport between the old town and the outlying parking areas, everything is within comfortable walking distance.