"The foul necromancers long ago perfected the alchemical treatment needed to turn a simple egg into a weapon of the most terrifying type. You know what a rotten egg smells like?" The old man didn't pause for an answer. "It's so much worse. The tales I've heard say that the victim of one of these eggs would tear their own faces off to try to end the smell." He finished the dregs of his drink, and waved to the bar wench for another. "The good news is that the eggs were as dangerous to the necromancers as they were to their victims."
"How so?" Allianora asked.
"Because they're just eggs!" A fresh tankard was placed in front of him. "Thank you lass! And eggs have a tendency to break."
"That's all well and good, but we wanted to know about the tower" Nimble grumbled.
"Aye, and why do you think that no one goes to the tower? Why do you think that no one has raided the vault? Maybe because there was a stash of eggs there, and at least one of them broke. It's been two score years, and the smell lingers still.
These corrupted eggs are potent weapons. Anyone within 30' of a broken egg must make a saving throw vs poison or flee the area and be so sickened that they will be unable to do more than defend themselves for 2d12 hours after. Anyone stuck by an egg must make a saving throw vs breath attack or cause themselves 1d4 points of damage and 1 point of charisma damage to themselves/round unless prevented from doing so. A successful saving throw means the character passes out for 1d6 hours as they're overwhelmed by the smell. In addition, anyone who survives will have their Charisma reduced to 3 until the smell is removed, and anyone within 10' will be at a -3 to all rolls.
To be rid of the smell, the victim (or area) must be washed with a special potion of cleanliness which can be created by anyone capable of casting remove curse, and brewing potions.