incredible ritual complex of thousand year old, suddenly abandoned Anasazi ruins, center point of a network of prehistoric highways, which retained their status as the largest buildings (that you probably never heard of) in North America until the end of the 19th century and the invention of steel skyscrapers.
Note: The roads from the highways to Chaco Canyon are intentionally left unpaved. They are rocky and can be hard to navigate for those who are unprepared for them. Also, once you get to the National Park, the nearest store or gas station is a four hour drive away. Bring everything you will need for your entire stay. Bring water for the trip in as well, but once you reach the park well water is available at the campgrounds.
People who like Chaco Canyon may also be interested in seeing some of the many Chacoan outliers, especially Aztec Ruins, which is far easier to get to. Ive also heard that Acoma Pueblo (Sky City) - is interesting, its another ancient pueblo - one that has been continuously inhabited since the 12th century. And of course Mesa Verde.