Geometry + Working Memory

Here is one to exercise your working memory while your spatial reasoning is engaged.

Imagine four or five solids (I used the sphere, cube, tetrahedron [a triangle-based pyramid] and cylinder, but don't let that influence you).

Now visually moving them around and scaling them, put the first inside the second inside the third inside the fourth. Now reverse the order of the nesting.

Too easy-peasy? Do it with more solids.