The Hungry Citadel

Where is this?
That's the problem, The Hungry Citadel was locked down in the northern reaches of the desert wastelands where the Great White Desert met the Iron Mountains. It is no longer there. Rumors abound that the Hobgoblin Warlord Kilthall was able to overrun the ancient Order of Mirra and unleash the all consuming fortress.
Why do the heroes want to go there?
The last time The Hungry Citadel was driven out of the wastes, thousands of people, plants, and animals were consumed to power the mobile fortress. The heroes have to stop the Warlord before she hits her target and consumes everything in this monstrosity's way.
What difficulties do the heroes face getting there?
Locating The Hungry Citadel is surprisingly easy. The black smoke it produces is belched hundreds of feet in the air and can be seen from miles away. Not to mention, the literal path in carves into the earth as it moves ever onward.
The hard part is going to be catching up to the fortress and assaulting a fully garrisoned fortress. This garrison most definitely includes air scouts, as they can be seen like vultures, always circling to find the Citadel's next meal.
https://dungeonmasterblock.freeforums.net/thread/1642/dm-nastics-87-journey-destination