If you happen to visit the phenomenal Glenstone Museum in Potomac, and you absolutely should, you’ll likely be ravenous after a few hours contemplating Ruth Asawa and Richard Serra sculptures; Andy Goldsworthy huts; and Jenny Holzer art.
You could hit the well-regarded Inferno Pizza a few miles north, but if it’s not open yet, your best bet by far is to swing by Gaithersburg’s Sunoco parking lot and order as much as you reasonably can from the Burrito Ranchero taco truck, which parks next to a fleet of U-Hauls and a convoy of cars waiting to be fixed.
Run by a family from Mexico, who has their own restaurant in Mexico City, Burrito Ranchero has been parking at the Sunoco for about six years. It also has an outpost closer to Baltimore in Damascus (45 minutes or so), plus another one in Germantown. Which is to say that you can find their excellent tacos without trekking to either Gaithersburg or Glenstone, though it’s a worthwhile field trip. (Glenstone is free, and you can see the massive Jeff Koons’ Split-Rocker, among other impressive works.)
When it’s your turn in line, order a quesabirria taco with consomé or the splendid al pastor tacos, plus some aguas frescas. Sit on one of the picnic tables installed under trees on a slope behind the U-Hauls.
While BR does not make its own tortillas—they know a good tortilleria nearby—the cooks griddle the pairs of tortillas, stack them beneath mounds of absurdly delicious stuff, then add all the things (radishes, cilantro, onions, grilled jalapeños, more onions, wedges of lime) plus little cups of red and green hot sauce. The results are beyond good.
There are other items on the extensive menu: carne asada, quesadillas, pechuga asada (grilled marinated chicken), tortas, lengua (tongue), carnitas, and so forth. There are also specials (eggs and sausage, steak quesadillas) that vary by location.
And, very happily, they have an excellent website with menus, maps, hours, and contact info—which means that you can actually plan your tacos, although that is not nearly as much fun as stumbling upon them in a parking lot when you’re tired and very hungry.
That’s the absolute best way of taco-ing, at least in my world.