I was exploring with some friends at a construction site, when I was nine or ten. There were some open pipes that were maybe 10 or 12 inches in diameter. I dropped a stone into one, and couldn't believe how long it took to hit the bottom. Two or three seconds. Three seconds would be around 140', not counting air resistance. Is that possible? I think they were building something tall, but it was a long time ago.
Not quite large enough for me to fit into, but still it gave me the willies.