Quoted from swolte:
With some experimenting, this should be simulatable. Like having a hidden teleporter that ends to a place in the Shadowworld with tons of goldmines. ......
Also you would need to use events to prevent the humans from finding a way to these gold mines... which should be in the caverns because spells and certain creatures can be used to sneak you into the shadowworld... unless anti-magic squares guard the caverns and surface from going to these shadowworld locations. It will take more than one event to stop humans from finding and using the teleporter.
There can be only one.
Highlander