Welcome to Phlebotinum Breakdown!
In a previous age a mighty archmage became powerful enough to create his own world. Seeding it with various forms of life he watched it bloom into a paradise.
When his homeland became threatened with destruction, the inhabitants fled to his newly created world seeking Sanctuary, which is what they named their new home. They adapted to their new home and built new lives for themselves. Many generations passed, and their original world became nothing more than a myth to them.
Now things are starting to go wrong. The weather has become fierce and chaotic, monsters are appearing in increasing numbers, and magic has started to go wrong in strange and unpredictable ways. It is as if the world itself is starting to fail and die.
A high fantasy campaign in which the ultimate goal of the PCs is to either fix the world or find a different world for the inhabitants to live on. The end of the world will be long and drawn out, so the PCs have as much time as they want to get distracted by random exploration or side-quests.
For those new to the setting, the wiki Main Page is a good place to start.