The Prado museum in Madrid is very impressive, with many works by El Greco, Velasquez, and Goya. There is a large, hilly park in downtown Madrid with a pond in the middle that is gorgeous as well.
Toledo is in itself impressive, as it is a walled city with steep roads originally designed to protect it against invaders. It is famous for its gold, which can be purchased (in the form of jewelry) for reasonable prices.
The mosque in Cordoba is striking in its size alone; it covers several city blocks. The inside is quite beautiful as well, with many shrines and elegant architecture.
The true highlight of the trip, however, was La Alhambra in Granada, a completely breaktaking palace with gardens, fountains, and amazing rooms set high above the city.
Quick Tips:
Though Madrid is supposed to be cool in March, when we traveled there, it was 80 degrees (F), which took us aback, quickly giving us all sunburns because we were unprepared. It is therefore wise to pack clothing and other items like sunscreen for a range of temperatures.
Vegetarians should also be aware that meat is a prominent part of the Spanish diet, and the alternative (especially if you are working with a set menu for the tour as we were)is usually an omelette. Vegetarian dishes can certainly be found, but they take a little work.
Best Way To Get Around:
We travelled mainly by tour bus, which was great, though public transportation is available in Madrid. The streets in many of these places are extremely narrow and curvy, however, so drivers unexperienced in European driving should be cautious.