I figured I wouldn't need four-wheel drive on this trip, but I actually managed to find a four-wheel drive road inside Grand Teton National Park. Just south of the intersection of Teton Park Road and Signal Mountain Road, there is a dirt road that heads east to the Snake River. After about two miles this road connects to the River Road. While most of this dirt road is in pretty good shape, there are a couple of steep rough sections where four-wheel drive is a requirement. There are many spectacular viewpoints along the remote River Road, and if you want to get away from the typical Teton crowds I highly recommend checking it out.