The pictures show a tunnel was used by Islamic State militants as an underground training camp in the hillside overlooking Mosul, Iraq. In less turbulent times, trains ran through it on their way to or from Mosul, but when the militants overran the area in the summer of 2014, they barricaded both ends, ripped up the tracks and built an assault course inside, on which to train their recruits. The tunnel - about 7 m (yards) high by 5 m (yards) wide, and around half a kilometre (0.3 mile) in length - features a series of obstacles, which one soldier tried out.