Marked singletrack loop through the grounds around the US Air Force Academy. Some steep sections and several road crossings.
I-25 to Northgate of Air Force Academy Non-Military Entrance - Exit 156B. Once you go through security, take your first left onto Stadium Blvd, then a right onto Academy Dr. -- Parking lot at the top of the hill on the right side of the road (near the stadium).
http://www.singletracks.com/item.php?c=1&i=10