As you focus your meditation on visualizing 4D objects, your mind begins to stretch beyond its usual limits. The concept of a fourth spatial dimension slowly starts to take shape in your consciousness.
You begin with a point, then extend it into a line, expand that into a square, and then extrude the square into a cube. Following this pattern, you attempt to "extrude" the cube along a fourth spatial axis.
Suddenly, a strange shape begins to form in your mind's eye. It's like a cube, but... more. You realize you're perceiving a hypercube, or tesseract - a four-dimensional analogue of a cube.
As you observe this impossible object, you notice that it seems to be constantly unfolding and refolding itself, revealing inner structures that both exist and don't exist simultaneously.