It's in the Flickr photo group, but I'll post it here.
Where is this place? I need a city and the name of this place within that city.
The first person to email the answer, gets his or her name listed on the sidebar for a week! Members of my immediate family are not eligible. Your user name is subject to change if I think it's unacceptable.
WINNER! - It's DXMachina, who correctly tabbed this as the Cahokia Mounds in Collinsville, IL. Specifically, this is called Monk's Mound and it is the largest prehistoric structure in North America north of Mexico City that is still extant. It is about 100 feet high and was built by an ancient culture called the Mississippians.
Presumably the staircase on the side wasn't built by them.