Select the Polygon Tool and draw a polygon of size 256 pt X 296 pt on the artboard. Turn off the Fill color for the polygon.
With the help of Selection Tool, select the polygon, and click on Object in the Menu Bar. Now place the cursor on Path and select Offset Path.
When you will click on Offset Path, a dialogue box will appear on the artboard. In that dialogue box, set the offset to -70 pt.
Check the Previewand click OK.
Select the Pen Toolfrom the Tool Panel and draw lines inside the inner polygon as shown in the below image.
Now select the inner polygon and the lines drawn. Then select the Shape Builder Tool and click on three parts of the inner polygon to make them individual shapes.
Now your inner polygon is converted into a 3D Cube.
Now we will fill color in the 3D Cube.
Fill the three sides of the 3D cube with lighter to a darker shade of the same color. (See the image below)
Now select the 3D Cube and press Ctrl + G to group it.
Select the 3D Cube and click on Effect in the Menu Bar. Place the cursor on Distort & Transform and select Transform.
When you will click on Transform, the Transform Effectdialogue box will appear on the artboard. In that dialogue box, set the Horizontal Move to 70 pt and the Vertical Move to -40 pt then set the number of copies to 1.
Check the Preview and click OK.
Now select the 3D cube, which is in the center, and click on Object in the Menu Bar. Then select Expand Appearance.
After expanding the appearance, Press Shift + Ctrl + G to ungroup the selection.
Now select the second 3D Cube and press Shift + Ctrl + M to open the Movedialogue box.
In that dialogue box, set the Horizontal Position to -70 pt and the Vertical Position to -41 pt then click on Copy.
Now select the third 3D Cube (newly formed 3D cube) and press Ctrl + [ to Send it Backward.
Now you can make more 3D cubes either with the help of the Transform Effect or with the help of the Alt key.
Select the third 3D cube and press & hold the Alt key. Now drag the 3D cubeto make a duplicate copy of it.
Make sure you place your 3D cubes inside the Polygonshape, drawn in Step 1. This polygon shape is your guide for the big 3D Cube in Illustrator made of small 3D cubes.
In this way make few more duplicate copies to complete your 3D Cube in Illustrator.
With the help of the Selection Tool, select the Polygon shape, and hit backspace.
Now select the Pen Tool draw a square as shown in the below image.
Fill the square with color #3b0709.
Now select the square shape and press Shift + Ctrl + [ to send it to the back.
Let the square shape be selected and reduce the Opacity to 48%.
Now apply the Feather Effect on the square shape.
Effect > Distort & Transform > Feather