The historic centre is small but extremely steep — Ouro Preto's cobbled streets climb and drop at angles that defeat all but the fittest walkers in a single day. Wear shoes with grip. Most sights are within twenty minutes of Praça Tiradentes on foot, but expect those twenty minutes to involve serious climbing.
Local buses run between the bus station and the centre and out to peripheral areas like Cachoeira das Andorinhas and the Mina da Passagem. Taxis are inexpensive and worth taking after a long day of churches; Uber works in town. For the steepest distances — the climb to the Capela do Padre Faria, for instance — a taxi up and a walk down is the sensible plan.