Downtown Santa Fe is walkable. The Plaza, the cathedrals, Canyon Road, and the Railyard are all within 15 minutes of each other on foot. Wear comfortable shoes — many sidewalks are uneven and the altitude makes a casual walk more tiring than you expect.
For Museum Hill, the opera, Meow Wolf, or trips outside the city, you need wheels. The free Santa Fe Pickup city shuttle runs three routes including a useful loop between downtown, Museum Hill, and the Railyard. Santa Fe Trails city buses cover the wider city.
Uber and Lyft work well in town. Renting a car is the simplest option for any trip beyond walking distance — and essential for day trips to Ojo Caliente, the pueblos, Bandelier, or Taos.