My ol' high school had HUGE ceilings in the library, prob like 30-40 ft. high. No ladder in the school could reach up there, they had to bring in special ones...
SOooooo, we bought a bunch of blow up dolls, filled them up with helium, and let them loose. They hung out on the ceiling for quite some time while EVERY student/teacher/administrator/etc made a special trip to the library to see what was going on.....
They eventually got in ladders that would reach the dolls....HOURS later!