Pärnu is flat and easy to walk or cycle. The old centre, riverfront, parks, mud baths, and beach are close enough to cover without public transport, though the beach area can feel farther in hot weather than it looks on the map.
Bicycles are useful in summer, especially if you want to explore the coast beyond the main beach. Local buses cover the wider city, but most visitors use them only for outlying neighbourhoods or bad weather.