The easiest legal border crossing between the United States and Mexico is the hardest to reach—but you'll be glad you bothered.
The only way to get to Jose Falcon's Restaurant is to drive for hundreds of miles from the nearest major airport (San Antonio, is seven hours away) to a national park (Big Bend) that bears the distinction of receiving among the lowest number of annual visitors in any park on the American mainland (roughly 380,000, by last year's tally).
Once in the park—a place that can take days to experience properly, due to its immense size—you drive for another hour or so, in the direction of the Rio Grande; you'll eventually see a modest sign pointing you toward the turnoff to Boquillas Crossing.
The road will dead-end at a newly-constructed Port of Entry facility, complete with proper parking lot—hop out, head down to the river bank and look for the guy with the rowboat. Unless, of course, you're here during the dry season, in which case you can pretty much just walk to Mexico.
That's not as dramatic as it sounds—its name may be the Rio Grande, but particularly when the water levels are low, it's more like the Rio Pequeño; there are many places along this wild stretch of the river where you could almost accidentally end up on foreign soil. (Don't. It turns into a whole thing, if you're spotted.)
Whether or not you take the boat ride ($5, usually, these days), you'll typically be greeted on the opposite shore by both a man who sings to welcome visitors, and a guide—these are amicable locals who will rather informally attach themselves to you, in order to ensure that your visit goes smoothly.
This is less an absolute necessity and more a byproduct of the fact that the tiny town of Boquillas del Carmen, where you are headed, is so far from civilization on either side of the border—the nearest town is 150 miles away, and takes hours to reach—that tourism has long been the lifeblood of the village. (The other bonus of having a guide—they'll take you to where you need to check in with Mexico's immigration officials—Mexico has in recent years become more rigid about documenting entries into the country.)
The trip into town—about a mile, maybe a little more, across a dusty elbow created by the river—can be done via pickup truck, or, if it's not too hot, burro, each for a couple more bucks; during the winter or whenever the sun isn't too strong, it's possible to walk.
The town, nearly abandoned after being cut off from the world for over a decade in the wake of September 11, 2001, has only recently come back to life; it remains a rather off-the-grid affair; what electricity there is comes from a newly-installed solar field. There are a few hundred people living here, for now, but in its entirety, Boquillas is pretty much just the one, unpaved road, lined with humble, one-story structures. There's a health clinic, a school—and, most importantly for visitors, a quiet cantina where you can do shots or grab a beer, and two restaurants.
The one you want is, as previously mentioned, Jose Falcon's, for hearty, borderland fare (green chile enchiladas, chile rellenos, burritos, and, quite obviously, tacos.) Get a seat up on the deck—there are great views of the river and Big Bend National Park, beyond—order a margarita, and forget all about how long it took you to get here.
For details about the border crossing, hours of operation and visits to Boquillas, go here.