Space Engine is incredibly unique and fascinating to explore. Many would say this isn't really a game, but at what point does it really matter?
Space Engine is a free 3D astronomy program and game engine developed by Russian astronomer and programmer Vladimir Romanyuk. Users can travel through space in any direction or speed, and forwards or backwards in time.
That vastness of it, while still retaining detail on a planet by planet level, is just outstanding. This game will give you a sense of how big the universe really is.