Practical notes
Two technical realities shape photography here: the Mediterranean sun turns harsh quickly after mid-morning, and the interesting surfaces are pale stone that clips if you overexpose.
Golden hour
Start about an hour before sunset. The light comes in low and lateral, which is what gives modernista facades their depth and the Gothic alleys their shafts.
Lenses
A wide angle for the alleys and interiors, a short telephoto for compressing the Eixample grid from the viewpoints, and a fast prime for the evening work.
Rules and etiquette
Tripods are tolerated in public space but not inside most monuments, and some churches ask for no flash. Commercial shoots need a permit from the city.