The Barcelona transport system is modern and reliable. The result: more time for exploring.
Many of the main attractions are close together. The famous Gaudi architecture is largely found in Eixample, which is close to shopping on Passeig de Gracia and La Rambla. A little way from there and you hit the Gothic Quarter and Placa Catalunya.
Walking Barcelona is certainly an option. However, if you prefer to get the underground, the Metro system is efficient and air-conditioned. The Metro stops at all the main attractions and you’ll rarely be waiting more than five minutes for the next train.