The door was made of iron, and wore a thick coat of rust. It was one of those doors, cast with swirling acanthus leaves, raised studs, leering goblin-faces and a grinning skull surmounting all.
It was sealed of course, hinges hidden on the far side, and investigation revealed no sign of lock or key hole, but the evil priest was somewhere beyond it and he was in desperate need of a good beating.
Then there was the ceiling. It was perforated at intervals with these troubling holes. Just narrow enough to prevent a gloved hand from exploring very far, torchlight revealed the slightest hint of something metallic waiting within each of these several dozen recesses. A trap.
Above the door, just about as high as a man could easily reach, a strange word was inscribed, each letter on its own dusty ceramic tile: WHAOXSDME
Holly the elf, one of the six adventurers gathered in the room, scrutinizing the lintel made a discovery; there was an inscription here!
In deep caves and in dungeons
I hide from the sun
Yet always I follow
No matter how fast you run
By noon of each day
I've shrunk to my least
But when the day dies
I grow long in the east
"It's a riddle!"
"And ... and if we get it wrong the spikes come down and ..."
"I can figure this out."
"Can you press the letters?"
"I'm going to start pressing a couple of them and see if ... "
"You don't use all of the letters."
"You've got to press them in order."
"I bet it's some monster. That doesn't sound good about the day dies."
"Are you sure?"
"Look, it's shadow"
"I press shadow."
DM: "So who is doing the pressing?"
DM: "It's a little too high for you to reach."
"I'll give her a boost."
DM: "Tell me exactly what order you press the letters in."
All Together: "S-H-A-D-O-W!"
DM: "Okay, Holly presses the letters one at a time. Hidden gears creek as the door swings inward ..."
Led by Holly the Elf (played by a very clever fourth grade girl) the party blasted through this puzzle in far less time than it took you to read this post (far, far less time than it took for me to think up a simple riddle and prepare a drawing of the sealed iron door).
My wife was in the adjoining room with the rest of the adults, listening in on the action. Also an educator, on the drive home she would point out that the players ranged from a 2nd grade girl to a 7th grade boy ... not usually kids who spend a lot of time playing together ... and that for those minutes at the table, they were fully engaged and operating as peers.
That's a pretty amazing testament to the power of the story-telling medium of paper-and-pencil tabletop RPGs to engage young people -- even those native to a digital era.