Stereoscopy is a way to see a 3D image on a 2D screen, which has been popularised by the Magic Eye books. You don't need any special glasses for this to work. It's a matter of training your eyes to do what you want. Gravit can display a stereogram of the simulation in real time by rendering two versions of the scene at once.
For most people, this is not an easy thing to pick up at first, so you'll need to learn how to see a stereogram. The link below describes a straightforward way on how to acquire the knowledge on how to view a stereogram:
There are two ways Gravit can display a stereogram of the simulation in real time. They are cross-eyed and parallel viewing. These two differs in the way your eye "joins" the image.
To get parallel viewing set up in Gravit, you'll need to get into the console using the ` key and type in the following:
stereo 1 stereoseparation -5
The stereoseparation value is adjustable, the more negative this number is, the more 'depth' you will see. The number actually means the angle difference between Gravit's eyes.
To get cross-eyed viewing going, the stereoseparation variable is positive:
stereo 1 stereoseparation 5
Increasing stereoseparation to a larger number will increase depth.