If you visit the big Spanish cities you can use its modern Metro service.
The most extensive network is that of Madrid 238 km long, founded at the beginning of the 20th century today is the sixth network in the world. They are followed by Valencia, with 175 km and Barcelona with 115 km.
There is also metro in the cities of Bilbao, Alicante, Seville Y Palma de Mallorca. In others they are building it or have it projected.
The best thing is that everyone is connected to the commuter train networks and urban buses and have special bonuses with discounts for tourists. This will then be a fast and economical way to get around in the big metropolis.