The dragon on the door was what was called a Precious Spirit.
Precious Spirits were as their names implied. There were made by mending the reminant spiritual energy of many strong ancestors.
This required a special method for it to work.
The Precious Spirit is born with a seperate personality but the same memories as contained in the spirit energies.
At a certain stage in cultivation, one starts to cultivate not just spiritual energy in the body but also spiritual energy in the heavens.
This incites heavens rage and a cultivator will have to face an heavenly tribulation.
When a Precious Spirit is made, it comes with a Precious Land.
A subspace different from the known world.
This was usually a land rich resources.
But there was just one problem.
The Precious Spirit was made from spirit energies of cultivators that have already touched heaven's spiritual energy.