What is a librería de viejo, and where are they found?

A "librería de viejo" is a type of used bookshop that typically specializes in rare and out-of-print books. These shops can be found primarily in Spain and Latin America, and are popular destinations for book collectors and enthusiasts looking for unique and hard-to-find titles. These bookshops often have a cozy and nostalgic atmosphere, filled with shelves stocked with old and antique books.