LEGO artist Carl Meriam has built a fully-working microscope entirely out of LEGO bricks. He was particularly inspired by the now discontinued LEGO X-Pod sets, realizing that the pods resemble a very deep Petri dish.
While trying to find a use for the pod itself, I realized that it was very close to a deep petri dish. I used a planetary gear system to allow both coarse and fine adjustment of the objective “lens.” A little more tinkering and I connected the focus to a magnifying glass and fiber optic light in the eyepiece, so adjusting the focus knobs would actually bring the writing on a LEGO stud in and out of focus.