The skyscraper

 Upon witnessing the tragedy of soulmates who died prematurely, the landlord created the skyscraper An entire universe in which he could rescue a select few, let them live the rest of their lives out in peace. In this skyscraper, there are a countless number of floors. Each floor its own world, with its own ecosystem and features. Some floors are vast, the size of entire continents with their own bodies of water, plants, and unique wildlife. And yet some floors are smaller, the size of small islands or villages, or even indoor floors that could just be a building, or a few rooms. Because of the variation and space in the worlds, societies and cultures have sprung up from the descendants of soulmates. 
The skyscraper is overseen by three people, the landlord, the custodian, and the doorman. While the Landlord created the skyscraper, the custodian and the doorman were once human, the first people brought to the skyscraper. They are there to help the tenants in their respective domains.