Past Seligman, there's a brief divided highway section that lets people turn in and out of Grand Canyon Caverns, a natural limestone cavern running 210 feet underground. The largest dry cavern in the country, Grand Canyon Caverns offers tours, horseback riding, a restaurant, and curio – curiosity – shop.
The lovely wide open spaces could also be a cause for concern if you're low on gas, so be sure to fill up in Seligman. Several small settlements, including Peach Springs, Hackberry, and Valentine may have a gas station here or there, but expect to pay a little extra!
Peach Springs is notable on the map for being the northern crux of this long, unique stretch of Route 66. In Cars, the fictional town of "Radiator Springs" not only resembles the name of Peach Springs, but also holds the same location on a map in the movie.
Peach Springs is the headquarters of the Hualapai Indian Reservation, through which this part of Route 66 passes.