Impossible staircase
Workers ascend and descend the breezeway staircase structure between the two dormitory buildings under construction, June 23, 2016 at the I.G. Brown Training and Education Center in Louisville, Tenn. Ladders and lifts (six in all) add to the building site's complexity, with the inner courtyard, and further still, the classroom building in the background. The facility will contain approximately 47,000 square feet of additional space on three levels and two levels with ten 20-person and two 100-person classrooms. (U.S. Air National Guard photo by Master Sgt. Mike R. Smith/Released)