My aunt is a world traveler who admires Diego Velázquez. What could she write in her blog after her trip to Spain? Caminé un día por en el museo El Prado.
Organicé un día por La Ruta de Sancho Panza.
Pagué por un boleto a París.
Visité la casa de Gaudí.

If she likes Velázquez, going to El Prado is a good idea. It's a Spanish museum, so Velázquez as a Spanish painter has several artworks displayed there, like Las Meninas. The other options don't work as well; B works better if she liked Miguel de Cervantes, C doesn't work because why would she go to Paris, and D doesn't work because Gaudí is a separate artist altogether.

So the answer is Organicé un día por La Ruta de Sancho Panza.

Explanation: