It's named El Taco de Mexico for a reason: Tacos are what this little Mexican lunch counter does best. All of the tacos on the menu -- from the most pedestrian shredded-beef variety to the gastronaut special packed with ropy calves' brains -- are as authentically Mexican as you're going to get this side of Tijuana. So is the eatery itself, a popular institution in Denver for over twenty years. The counter is long and usually packed with demography-confounding customers who know the real thing when they taste it, and the open kitchen is filled with busy women abusing various hunks of meat with giant cleavers, then stuffing corn tortillas with all manner of beef, pork and chicken parts and topping them with shredded cabbage. The only add-on is chunks of lime (on request), but that's all the help a true taco ever really needs.