Molith is a 3D game made in the Unity engine.
It's available to play for free here.
This was made in a couple of weeks for the Frogwell community Secret Santa gamejam. Prompts were written by participants, and randomly exchanged amongst the group.
We were given the following prompt by fellow game developer HumanIsRed:
Dear Santa,
I wish for a game that features a megastructure! What you do with the mega structure is up to you. You can manage it or simply navigate it but it must be a central part of the gameplay and you must FEEL the sheer size of it.