The Narrows are located in Zion Canyon. The gorge’s walls can reach 1000 feet high with only 20-30 feet between them.
Here’s a brief video showing The Narrows:
Hike the trail in late summer when the water is warmer and lower than earlier in the year, so that you can wade into the narrows. When water levels are too high or flash floods occur, the park services closes the trail.
Learn more about national park day hiking trails in my Best Sights to See at America’s National Parks guidebook.