Art by Bethany Berg

On the high plateaus of the roof of the world stands the spire of Tour Toriel, a tower of rock and ancient ruins that predates all of recorded history. Within the fortress that clings to its unassailable slopes reigns the Dread Tyrant, whose power is so great that every kingdom and city in the land has bent to his dominion.

One year ago, a terrible purple vortex opened in the sky above the spire. Harvests began to spoil in the fields; unspeakable new monsters spilled out of the wilderness. The wise women, the priesthoods, and the scholars cannot explain what is happening, but all signs are clear as to the source: something in Tour Toriel has gone awry, and will destroy the world if it is not stopped.

You are a band of heroes dedicated to finding out what has gone wrong in the spire and stopping it. It is almost certainly a suicide run, but doing nothing is only a slower death.

You have discovered a secret entrance to the caves under the mountains upon which the spire rests. Your plan is to delve this dungeon and work your way upwards into the castle. There, by hook or by crook, you will discover the source of this calamity and--hopefully--the means to end it.

Let's play Cortex.

Keystone is a fantasy roleplaying game primed for Cortex that is also a step-by-step tutorial for learning how to play Cortex. The first adventure is free to download and play, and has all the rules you'll need included in the document. Two more adventures are available, and two more are in development.

You can get all of them at

Or grab them all in the Ascent to Prime bundle.

Keystone is Primed for Cortex, the award-winning world-building tabletop RPG system for forging unique, compelling game experiences from a set of modular rules mechanics. If you have questions about Cortex, get answers on the Cortex Roleplaying Discord.