Follow a short path to a steep zigzagging stairway that takes you past military equipment as you make your assent. At the top, atomic cannon 'Atomic Annie'— and a great view of I-70 and the city—await you. The cannon is remarkable—42-feet in length, 42,500 pounds in weight, and can travel 35 miles per hour. The big gun was activated in 1952 and deactivated in 1963.