Sagrada Familia

If you have time for only one sightseeing outing, this should be it. La Sagrada Família inspires awe by its sheer verticality, and in the manner of the medieval cathedrals it emulates, it's still under construction after more than 100 years. When completed, the highest tower will be more than half as high again as those that stand today. It attracts around 2.8 million visitors a year and is the most visited monument in Spain.