Artemis' Pact just finished.  In that adventure I established "Stargazer Hill", a mound in a clearing not far from Daunton where the night sky is easily visible.  A tunnel leading into the hill and coming out in an Allarian silver mine just opened up.  We're done with the tunnel for now, but I was thinking about how it could be further used:
In this post, 7 Rabbit and Lilli are claiming the site for the IAC.  It might be neat to set up a full archeological base camp, with mages making sure the portal doesn't close and sending teams of adventurers into the caves looking for the 
underground passage, a land route to Allaria.  Or maybe underdark creatures could wander out of it, so we need to set a guard.
But I originally stole the name Stargazer Hill from Sleeper in the Tomb of Dreams, an adventure for 8th-level characters from Dungeon #155.  So another neat way to go is for the magic passage to collapse, but find out that it was hiding a 
normal passage into the hill.  The IAC could clear the layers of earth from the hill and find out it's a giant face, and then send adventurers in to explore it, leading to the 8th-level adventure.
But doing this would lose the passage to Allaria, which has other fun possibilities.  What do you think?