The five of you have been drawn to this location for reasons of your own, but are ready after lunch in the Wizard's Tavern to meet the Wizard himself.
"Welcome heroes. I thank you for answering the call. As you may know, my family labors under a curse from Asmodeus himself. He tasked each of my ancestors to build a level of an evil dungeon. This curse will be broken once a 14th level is built. I am Gorthaur the 14th, and I need brave volunteers to clear a way through the devious dungeons designed by my forefathers. It will not be without recompense!
Doubtless many treasures and magic items have been stashed in the dungeons, and you are welcome to all of them. I will identify magic items for you at the low cost of 100 gold per item. I sell spell books at the standard prices. Your rooms will be securely wizard locked and can only be opened by myself, or the person I attune to the lock. All I ask on my part is 10% of the value of gold and gems as my cut for lodging you, and that money goes towards my building fund for the 14th level.
You may find various personages looking for adventure and money to help you in the dungeon below - the tavern will be sure to find most of them. I suggest the five of you band together - the levels are doubtless dangerous."