This trail is hiked by nearly every visitor in the park, so it can get crowded. However, the scenery is superfluous, spectacular, and severe.
From the Santa Elena Canyon parking lot at the end of the Ross Maxwell Scenic Highway, follow the trail to Terlingua Creek. Occasionally the park erects a bridge across the creek, but it is usually not there. Wade the creek (it is usually only ankle-deep and clear). If the creek is deep, muddy, and swift, do not cross it.
After the crossing, continue on the trail to concrete steps which take you up to a viewpoint into the canyon. This canyon is just HUGE. It's not nearly as wide as the Grand Canyon, and only half as deep, but the narrow walls and unbroken cliff faces make it EVERY bit as overwhelming.
The steps descend to a beach on the river inside the canyon's mouth, and ends shortly afterward.
Despite the crowds (and "crowd" is relative...on its busiest day, there are a FRACTION of the people here that you'd find on the Bright Angel trail in Grand Canyon, or Half Dome trail in Yosemite) this trail is a MUST for any Big Bend visitor. Enjoy!