Colossal Cavern is a name of power, whispered in dark corners, embodying incredible riches and untold danger. Sensible folk hold this cave to be a myth, the product of fevered imaginations - but every year a handful of people set out to find it, driven by necessity or by overwhelming greed.
Most return empty-handed with tales of fruitless wanderings, or lies about the dangers faced: volcanos, dragons, gigantic snakes and the like. But some have never returned, and speculation holds that they are the successful ones who have found the cave and perished - or maybe used the enormous wealth from it to found great empires in far-off lands where they live in luxury.
Thus it is a unique event when a travel-stained warrior enters the tavern where you are sitting one evening, pays the inn-keeper with an absurdly high value gold coin, and over his drink claims that he has visited Colossal Cavern - and escaped with his life!
The other drinkers flatly disbelieve him. "Thief" and "mercenary" are two of their more flattering suggestions to explain his wealth, but you are not so sure - for he has a haunted look and refuses to discuss his exploits. Thus, when you realise that an ambush is being planned to deprive the stranger of his money (and life) you lead him out to safety by a back route.
"A thousand thanks!" he exclaims when the sounds of pursuit finally die away. "May the Gods smile upon you for your deed tonight! But I fear that your friends may seek revenge if you return."
"Thus, to reward you for your valour, I will give you the most valuable treasure that I own... the location of Colossal Cavern!"... and he presses a crumpled scrap of paper into your palm. Frankly, you were expecting hard cash - and a lot of it - but he looks like a good man in a fight, so you accept the meagre reward and even manage to shake his hand warmly.
Despite your natural suspicions that the map may be a fake, it would be foolish to stay and face the wrath of your fellows, so you set out to follow it. And the map turns out to be genuine! It leads you through uncharted lands: over mountains, through forests and skirting deserts - always avoiding the inhabited places of the earth - until one day's journey would bring you to Colossal Cavern itself.
Then disaster strikes. You are leaning on the wall of a building from which a river emerges and follows the road south. To the north is open country and all around is dense forest. As you attempt to decipher the next part of the map, a freak gust of wind lifts it from your hand - and carries it into the water. Rescue is not possible for the river sucks it down instantly, and in any case you cannot swim.
The next part is up to you: to find the Cavern, enter it, and return with its treasure. And, as you stand thinking, you remember a scrawled note on the margin of the map:
"Warning. Magic works in the Cavern!"