Circuit de Barcelona-Catalunya
The Circuit de Barcelona-Catalunya is obviously located in Barcelona, in the Catalonian region in the north-east of Spain. It is a relatively new circuit, only built in 1991, the year before the Olympic Games took part in Barcelona. It is since then the home of the F1 Spanish Grand Prix.
The circuit should not be confused with the Montjuïc circuit, which hosted the Spanish Grand Prix four times between 1969 and 1975 and, unlike the Circuit de Barcelona-Catalunya, is actually located within the city of Barcelona itself.
The 4.675 km (2.905 mi) motorsport race track combines a fast long straight with a variety of flowing corners, making it an all-rounder circuit. Add to this fast-changing wind and weather conditions, which could dramatically affect the strength of a given setup or tire compound, and then you understand why this circuit has been for many years the location for the F1 pre-season testing.
Some more resources for a deep dive: