It was shaped like a hollow egg, with the world inside and the land consisted of floating islands.
One day while the rest of the party was resting after a particularly unpleasant encounter with a lich (he insulted them mercilessly), the monk went spelunking.
Now, this monk was played by the younger brother of a friend (you probably know the deal), and he was one of the more chaotic characters I've ever had to run for, but it was all fun so we didn't give him a hard time about monks being lawful.
But when the player discovered that his monk was suffocating because the islands were full of hydrogen (the coral worm that creates the rock also secretes hydrogen, which is imbued in the rock and makes the islands float)...
....it was entirely reasonable and in-character for the monk to "accidentally" break a flask of alchemist's fire to try and burn away the gas, without considering the consequences.
The cleric got into his bag of holding, all but his head so he could still get out, and took a nap (Concentration checks required, naturally) so he could prepare spells.
With his newly prepared spells, he cast divination to check if his assumptions were right, and then banished himself.
As a creature not native to the elemental plane of air, he was summarily returned to his home plane.
A bag of holding with a head sticking out of it popped into existence ten feet above the ground in the square of his home village on the material plane, falling at terminal velocity. It hit hard enough that he fell all the way into the bag and it closed up, trapping him.
He sat there waiting for someone to come along and open the bag, but was running out of air... so he cast create water and water breathing.
This gave him enough time for someone to open the bag, producing a sodden cleric.
However, he'd banished himself right out of the game and had to roll a new character.
@AlexP Drow monk and catfolk ranger were also on the floating island when it exploded.
The catfolk pulled out his blanket and wedged it under his chestpiece to fashion a crude flying-squirrel type wing.
The drow tossed out his amazing arsenal of blades (accidentally killed a dragon with a flying katana and leveled up partway down), and joined the ranger by clinging to his legs to form the tail of their kite.
They managed to slow their decent and gain some control over the fall, guiding themselves towards the eye of the eternal storm at the bottom of the world.
However, the storm at the bottom of the world was the only source of water, and so it was a shipping lane for flying ships. Run by the evil elven empire.
So the ranger and the monk steer for the ships rising up through the eye of the storm. First ship they almost hit: rip through its wing and keep on going.
Second ship they hit the deck, tumble, drop off the side, grab the rigger, and climb back on board...
...just in time for the ship's wizard to come up from his lunch belowdecks and hit them with telekineses to shove them off again.
Now the monk and ranger were getting close to the continent that floats in the storm. Rising up from the ground are enormous golden towers shaped like arms sticking up out of the soil, with hands open to cradle the ships.
They aim for one of the hands. The ranger hits first, botches his roll and goes splat on the golden palm after the damage from slamming into both ships.
The monk rolls astonishingly well and manages to use his slow fall ability (reduce falling damage by X dice if you're adjacent to a wall when you fall) to slow his decent along the side of the arm.
I start counting out dice based on falling distance and slow fall. He rolls Tumble to remove a couple more dice. I roll damage... get very low numbers. He hits the ground with 0 hp.
Takes a moment to catch his breath, is greeted by the first of the new PCs the players have rolled up while he's been falling... and hears a CRUNCH up above.
Looking up, the new party sees the flying ship whose wing they'd torn through spiral down and crash into the ship they'd been shoved off of by the wizard.
Both ships begin falling at an alarming rate toward the party, which scrambles for cover.
End scene, next session starts in a cave inside the continent, I have to throw out all my notes about the campaign we were going to have a week's flight up there.
