Barcelona is on the Mediteranean coast of Spain. Many of Barcelona's tourist attractions are the works of Antonio Gaudí, an extremely unique architect that lived from 1852–1926. Gaudi has many significant buildings throughout Barcelona and those buildings tend to be some of the more popular touist destinations.
The most visited attraction in Barcelona is Gaudi's Sagrada Familia. Gaudi started work on Sagrada Familia in 1882 and it is still under contruction today, and will remain under construction for years to come. It is certainly unlike any other cathedrals in the world and it is worth a visit.
Another interesting attraction is the Christopher Columbus Monument, which was erected because Barcelona is where Christopher Columbus reported to Queen Isabella Columbus returned from discovering the Americas.
Barcelona is a popular cruises port, with a fair number of cruises starting and/or ending their voyages here.
The Barcelona metro system is good and, at least on my trip, always got us very close to the attractions we wanted to see.