Dotus
From ROI Wiki
Dotus is the homeworld of the Yandians and is also home to the Master Database, the store of all knowledge collected and held by the Yandians. And, while the entire planet is covered in one massive, world spanning city, very little of it is visible as most of it is built below ground to protect the natural environment of the planet above, as the Yandians love nature and go to great lengths to protect it.