The Mindbender is the world's largest indoor triple-loop roller coaster located in Alberta, Canada. The 1986 accident occurred when the coaster’s fourth car derailed before encountering the third and final loop. The train failed to clear the loop and slid backwards, crashing into a concrete pillar. Four passengers were thrown at least 25 feet to the floor below. Three died in the incident, the fourth was rushed to hospital in critical condition.