The King of the Island Nation of Thalass has gone missing and his Queen is willing to pay handsomely for his return. The King’s last known location was on a small island where according to legend a gate to another realm exists. The King left with his most trusted advisors and soldiers in hopes of finding his way to this realm in order to gain a weapon or artifact to help him safeguard his people from the other nations of the area.
King Thalass, as all Thalassian kings are called, had been convinced that his small kingdom would soon be overrun by pirates and invading forces if he could not find a way save them. As a result he fixated upon the ancient legend of The Anagen Gate. A gate through which a person may pass to find new power and strength, strength King Thalass could use to protect his kingdom.
The Queen knows the location of the island where King Thalass was headed and can give this to the heroes. The trick to the Anagen gate though comes from the fact that once you go through it, you can not go back out the same way. Any who enter may only return to their own world by going forward, through six more gates. Each gate takes the traveler to another realm where they must prove themselves worthy to move forward and only by making it through the seventh gate does one return to the island.
When the heroes arrive the King is stuck just inside of the third gate, where the last of his advisors was struck down. Each realm has its own challenges and problems to solve to make it through the next gate but once the King is found, and the heroes convince him that they are both real and on his side, he will willingly work along with them to make their way out.
There is plenty more to flesh out here, each realm could be a single encounter or an entire adventure for the players. The rewards for any hero making his/her way through the final gate could also vary greatly. The reward could simply be the experience (and new power gained thereby) or could be strange new abilities or magical items. Once the King is returned there could still be more to do as well. Where did he learn of the legend? Was it planted for him to find by an enemy nation or by a rival within his own kingdom, hoping to usurp the throne in his absence?
I think lots of fun could be had working within the framework of this adventure hook, but what do you think?