Doing this in Catalonia is one thing I truly recommend. Barcelona is a great city, with lots of landmarks and many things to do, but if you are spending more than 4-5 days there it would be great to get on a day trip to explore the beautiful landscapes and old towns in Catalonia.
The best way to do it is to get a guided tour that lasts for about 10 hours, check the offers on sites like Viator and you can get some good deals. There's also the possibility of renting a car and exploring the region on your own, this way it's more flexible, but not having a guide can be a downside.
What should one visit in Catalonia?
Girona, a city with a long history, believed to be founded around 76 BC. It has a great medieval city center, with narrow streets and gardens near the old city walls. Some attractions are: the remains of the roman walls, the hanging houses(cases penjades) on Onyar River, the old Jewish quarter and Saint Mary's Cathedral.
Cases penjades in Girona 
Girona Cathedral Montserrat, one of Spain's most important pilgrimage sites for hundreds of years, due to the famous 12th-century Romanesque carving of the Virgen Moroneta, the Black Virgin. The abbey is situated on this multi-peaked mountain.
Montserrat AbbeyPals, a small city that developed near an old fortress. The Gothic Quarter of Pals is a great tourist attraction. By visiting the fortress you also get a great view of Costa Brava from the old observation Towers.
Street on the Gothic Quarter of Pals Costa Brava. Visiting a city on the shore should be mandatory on a trip like this and Calella de Palafrugell is a great example. You can explore the rocky coastline, take a bath on a secluded beach, admire the whitewashed houses that almost reach right down the seafront. There are some great restaurants on the beach so it's a great place to have a meal and admire the sea.
Calella de Palafrugell 
Calella de Palafrugell beach 
