Out last trip to Big Bend, we got to take a float trip down the Rio Grande River. One of those bucket list days. The river was high, light clouds, not too hot or too cool. The river flows through some narrow canyons in this area.
And nothing says narrow any more than a slot canyon. The top of this one is accessible from Texas FM170, which in my book is the most scenic drive in the state. The bottom end of the canyon is accessible where it runs into the Rio Grande. The only way to get all the way through is to be an experienced rock climber and have gear with you.