Sloping tops: while most lockers have flat tops, some manufacturers offer the option of sloping tops to their range of lockers. The slope may be of either 30 degrees or 45 degrees to the horizontal, sloping towards the front, and the purpose of this is to make it impossible to store items on top of the lockers, or to make it harder for dust or other debris to accumulate there. This is an important factor in places like food-processing factories or restaurants where hygiene requirements must be met.
There is a luggage storage service a short one minute walk from Union Station in downtown Denver - LUGDEN. You can make a reservation online - lugden.com, call - (303) 747-5600, or show up as a walk-in. They offer hourly, day, overnight and weekly bag storage. Great place to store your luggage if you're on a layover from Denver International Airport, or going to a concert, or headed to a Rockies game at Coors field and want to enjoy yourself without having to lug your bags around.