A line forms in the street for this taco spot just half a block off the Zócalo. Bring cash, then order at the small entrance where you'll be given tokens to give to the taquero to indicate how many tacos you've ordered. While the menu is limited (you'll choose from potato, beans, carne en adobo, and chicharrón with salsa verde), these are some of the least expensive tacos you can find, so go ahead and order with abandon.
The line moves quickly and once you're inside, the dining room is deceptively large. Sit or stand, but don't skip the salsas, pickles, sliced cabbage, and guacamole to top off your tacos.