This cache is part of the series using themes from the Dark Tower Series by Stephen King, a seven-book story described as a sci-fi western set in an alternate universe. In the series, traveling companions Roland, Jake, Susannah, Eddie, and Oy become hostages of a self-aware monorail named Blaine hell-bent on committing suicide in a failing world. Blaine remarkably resembles a character from a book called Charlie the Choo Choo, which was pointd out by Jake to have an eerily creepy, not quite joyous, smile. Jake didn't trust Charlie, and he was right to be suspicious of Blaine the Mono too.
The ka-tet (or group, in High Speech) must out-riddle Blaine for the chance to survive the ride. Some of the most entertaining riddles from the exchange (in my opinion) are as follows:
"When is a door not a door?"
"I occur once in a minute, twice in every moment, but not once in a hundred thousand years. What am I?"
"Why do people go to bed?"
"Why did the dead baby cross the road?"