The Garden is entered via a portal on Mars, only accessed with the eye of a gatekeeper. It consists of vegetation and fauna not unlike what is seen on Venus. Vex Goblins covered in roots and vines ominously litter the sides of the path, and in several instances spring to life.
Vex resistance is heavy, and for good reason. The Exo Stranger describes Black Garden as a realm in which the Vex are mass produced, and further alleges that it will be Humanity's undoing. Upon first arriving, your Ghost describes that through diagnostics it appears you've entered another dimension and he cannot pinpoint your location in the world.