If you want to do a traveling trip to Spain but you don't feel like it rent a car, what I recommend is getting around the buses. Among the various companies that offer services to the major cities of Spain it is good to remember Avanzabus.
An example? From Valencia to Madrid to 30€ do a roundtrip, the travel hours are only 4 and there are several special rates, such as for children under 20 or for children, under 4 years in fact the ticket price is half the price.
Another example. If from Madrid you want to get to Lisbon it will take you 5 hours by bus and 40 € for a round trip. The price is very valid since with the plane you would spend much more and in addition there is also the "night" with departure at 21 and arrival at 4.30.
Many routes are proposed, including short-haul, also fromMadrid airport directly to Benicassim or Salamanca. Last curiosity for families, i children under one year old, they travel for free :)