Yggdrasil

Yggdrasil (very Norse inspired) the world tree. A tree of portals that connect s to other planes of existence. Because it connects to so many worlds it only makes sense that a city would form inside and on the tree. The city is make up of all types of planer beings.
Why wouldn't an adventurer want to come here? This is a city of portal! There's adventures for eons here!
The trick is getting there though... many folks of the material plane make pilgrimages here but few make the journey. (One does not simply walk into Yggdrasil) unless you find a portal or teleportation circle I suppose. But for those low level characters brave enough to journey through the monster infested sea that surrounds the tree. And if they survive that they must make their way through a hedge maze with strange fey ready to play tricks on pilgrims.
https://dungeonmasterblock.freeforums.net/thread/1642/dm-nastics-87-journey-destination