Old Ruins = Old Enemies

"How did they get here?" Logen was shouting at Bayaz.

"I can only guess," grunted the Magus, wincing and breathing hard. "After the Maker's death we hunted them. We drove them into the dark corners of the world."

"There are few corners darker than this one." pg. 374-pg 375

"Not quite so empty as we thought eh?" pg. 410

It's a classic cliche that the old ruins of the world are inhabited by the things that are not allowed to dwell where man does. After all, why would those monsters be anywhere else? Is the balor going to take up residence in the elf town? If the great wurm going to act as a city guardsman?

More importantly though, these are places out of the way. These are places where evil can grow unchecked until it spills unto the rest of the world.

These are places where the foolish and adventuresome go and if they disappear, well, who knows better anyway?

Remember the old places of the world and the old powers and old treasures and even older horrors that might wait for the ambitious but remember to have it tie into current campaign events in some way.

In 4e for example, these lost ruins could be the former cities of the older primal beings whose followers were hunted out of the civilized lands. In the dark parts of the universe, those magi and angels and forces of light may have banished those dark and cruel entities to further realms. In the old 3.5 timeline, there was an invasion that took care of the current entities of the Abyss, the demons before the tanari. This was some good fiction taht the author put to use in his Green Ronin book of a similiar nature.

Things older than demons, things of an older nature than the Abyss. Things with darker ways and darker paths.

The world is vast and ancient and the adventurers that do not respect it will fall to it.