Potosí's colonial centre is compact and walkable, though the altitude (over 4,000 metres) makes even short walks feel strenuous until you acclimatise. The historic core — the area between the bus terminal, the Plaza 10 de Noviembre, and the market — can be covered entirely on foot.
Minibuses (micros) run fixed routes across the city and are inexpensive. Taxis are available and cheap by any international standard; agree on a fare before getting in. The bus terminal is far enough from the centre that a taxi or minibus makes sense with luggage.
For the Cerro Rico mine tours, transport to the mine entrance is included with most organised tours. The Khari Khari Lakes require either a hired taxi or a long walk; most visitors go with a tour agency.