Barcelona –Lots of tourists; Las Ramblas was a great street to walk and sightsee, and the street markets are awesome. Check out the hundreds of beaches along the Costa Brava and the architecture of Gaudi, which transformed Barcelona.
Bilbao–This town has amazing architecture, but is mostly known for the incredible Guggenheim museum.
Cádiz-Beach destination, kinda resort-ish, but Carnival was one fun party. We booked an all-inclusive 3-day package trip with Funiversal travel agency for Carnival weekend.
Gibraltar-This only thing worth doing here is climbing the ‘rock,’ seeing the caves and the monkeys. Otherwise, there is not much else. Most people come here to take a ferry to Tangier, Morocco. We recommend that you go with a big group to take advantage of the group rates and to take necessary safety precautions.
Pamplona–It is famous for the running of the bulls.
San Sebastian– Amazing tapas and a beautiful scenic beach town, plus good surfing.
Segovia – (NYU usually takes students here the first week.) Quaint town close to Madrid with a stunning castle and church. Absolutely beautiful town to visit. It also has an amazing Roman aqueduct!
Sevilla-Great culture stop, picturesque gypsy/folky Spanish, historic Andalucía (great during Holy Week). There is a 2-hour high-speed train from Madrid. We recommend the sightseeing bus tour there. It was cheap and actually very informative and went to all the interesting and historical places with freedom to hop on and hop off wherever and whenever you want.
Toledo– (NYU may offer an optional trip here during the semester.) Quaint and stunning town close to Madrid with much history (old capital) and a very unique handicraft. They make beautiful pieces out of black metal with gold inlaid designs. It is an incredible place to wander around, but be prepared for the steep hills. Also, has a very interesting rich Jewish history. Make sure you see the old temple.