A car is strongly recommended for exploring Galicia. Public transport between the main cities (Santiago, Vigo, A Coruña, Ourense, Lugo) is reasonable by bus or train, but reaching coastal villages, inland valleys, or sites like the Ribeira Sacra or Castro de Baroña without a car is difficult. Bus company schedules are often not online, and services are infrequent outside city routes.
Renfe runs trains between the main Galician cities and connects to Madrid and the rest of Spain. The train from Vigo to Porto (Portugal) is a useful cross-border route. Ryanair and Iberia serve Santiago de Compostela airport, with connections to Madrid, Barcelona, London, and a handful of other European cities.
Within cities, Vigo and A Coruña have decent bus networks. Santiago de Compostela's old centre is compact and best explored on foot.