The Narrows is a famous hike up the Virgin River in Zion National Park. Its extremely popular but if you happen to do it in January when its about 0 deg C you will likely be the only person in the canyon. With the proper dry suits and doubled wet socks and boots, wading through the freezing water is doable. In some points it goes to chest level. Round trip it took 6+ hours. By then my body core had dipped too low and got the body shakes. Regardless, it was well worth the effort! Hiking a slot canyon with 1000 ft cliffs on either side is an absolute amazing experience, especially when you can do it without the crowds.