4-D Universe

Salvador Dali, one of the greatest painters of the world in 20th century, loves high-dimensional abstract concepts. Many of objects and ideas in his works can only be realized in a wolrd with a dimension higher than 3. One example is that one of his late work, the hypercube cross, in which the cross is consist with 8 cubes. The 8 cubes together actually represents a cube in a 4-dimensional space. Or more exactly, it is an fold-out in 3-dimensional space.
To understand this point, we can apply the same method to construct a 3-d cube from six 2-d 'cubes', i.e. squares. That is the way how a box can be built out of paper.

Instead of using squares, we can also use pentagons to construct a 3-d object and we will get a solid shape called dodecahedron. And 12 pentagons are needed for the purpose.
Like that 8-cubes can construct to a hypercube, can we get something interesting if we were able to stack many dodecahedrons together in a 4-d space? The answer is yes. The object is called '120 cells'. It needs 120 dodecahedrons to fill all the space inside. You may wonder how to imagine how such a object look like...? Well, you need to put five layers of dodecahedrons on top of each other and you will get a fold-out represenation of the object, just like the Dali holy cross for the hypercube. Then, in the four-timensional world, you need to squeeze the dodecahedrons and stick the faces of the dodecahedrons together. Below is a beautiful picture of the fold-out version of the 120-cell available from Wikipedia.

120-cell made with 120 dodecahedras, projected in 3-D space and depicted on a 2-d sheet.