So your PCs have won their quest, be it slaying a mighty dragon with a magical weapon of old, beating a crime boss, or vanquishing a mighty wizard or wight, and they have taken possession of the treasure. Chest after chest of gold and silver coins, gold bars, and every kind of jewel and gemstone is theirs for the taking. If they are not careful, they may find that their trouble has only just begun.
The city was cursed many years ago. Since then it has not stopped raining. The gutters are inhabited by eels and the doors are on the first floor, coated with pitch. On a bad day, you can see the water level rise above the ground floor windows. Carts have both wheels and bladders filled with air to keep them afloat. And yet everyone is surprisingly dry.