The word "tianguis" comes from the Nahuatl language of the Aztecs, and it has been a part of Mexico's culture for time immemorial. Every neighborhood will have at least one weekly "tianguis". In Nápoles there are two (if not more) markets each week. On Sundays there is quite a large "tianguis" in which the street just around the corner from my apartment is closed to traffic and filled with market stalls.
On Thursdays there is a smaller market. In this case, the street is not blocked off. The vendors' stands are set up on the sidewalks on three sides of the neighborhood park. Here you find not just fruits and vegetables, but everything from shoes to underwear to houseplants. I know that I have written many times about the markets in Mexico, but whenever I see one, I cannot resist taking more photos.
This fellow was frying up "chicharrones" (pork rinds).
If shopping makes you hungry, the "tianguis" always has places where you can eat, such as this taco stand called "Tacontento"... which is a play on words. It could be taken to mean "Taco contento" ( Happy taco) or "Está contento" (He or she is happy).