What is a librería de viejo, and where are they found? Write your answer in English.

A "librería de viejo" is a type of bookstore commonly found in Spain and other Spanish-speaking countries. Translated as "used bookstore" or "second-hand bookstore," a librería de viejo specializes in selling pre-owned books, both rare and popular. These bookshops often have a unique charm as they carry a variety of literary treasures, including out-of-print editions, vintage books, and antique manuscripts. Librerías de viejo can be found in major cities and towns, usually in the older parts of town or cultural districts, where book lovers can browse through shelves filled with literary gems, collectible editions, and forgotten titles.