If you’re ever in a city for just a day to see it, one very good option is to hop on to a City Sightseeing bus. This company operates in many cities around the world and for a modest fee you can ride on these buses for the entire day, hopping on and hopping off at it’s many stops. It’s probably best to plan your trip beforehand by downloading the route from their website and working out where your hop-offs will be. The prime seats are on top, right in front and as such are very popular. My advice would be to ride up top for one entire circuit then start your hopping off afterwards. These buses come with optional commentaries in various languages and can be pre-booked on their website to save you time and money. I rode one in Barcelona and Madrid when I was in Spain and it proved to be a very economical way to see everything I wanted. The one in Barcelona even went as far afield as Parque Güell. Note that City Sightseeing is one of several companies – it might pay you to shop around for the best one for you.