1. Loot and burn down the tower.

Haven Lands. There is an old, crumbling stone tower at the end of this valley. It is speckled with mud and slime. No humans have been up here for many a year.
[1. Explore the tower.]
Inside the tower, you find abandoned living quarters and a surprisingly intact alchemical workshop. Someone spent many years making potions out here.
[1. Examine the equipment.]
You can't tell when the alchemist left. It's been years, at least. Whoever it was, they left fast. The shelves rotted, the jars fell to the floor and smashed, and the goo inside oozed into the ground.
You find one thing of value: a potion flask, miraculously intact and still sealed.
[1. Take the potion.]
It is a properly enchanted potion flask. Seems like it will be very useful. You put it in your pack.
[1. Loot and burn down the tower.]
First, you help yourself to everything you can sell. Then you light a torch.
The goo and slime is surprisingly flammable. Soon, the tower is ablaze. The vile stuff will no longer seep into the earth. Maybe, in a few years, nature will reclaim this accursed valley.
As you run out of the tower, you find an unpleasant surprise. The heat and vibrations have caused several towers of goo to rise out of the earth.