An Experimental Demonstration of Evolution.
Make a GIANT Petri dish.
Divide it into strips. As you move towards the center, increase the concentration of a simple antibiotic by a factor of 10 on the strips (so it goes 0, 1, 10, 100, 1000, 100, 10, 1, 0).
Add E. Coli bacteria to the outermost strips.
Put a time-lapse camera where it can look down onto the whole dish/plate.
Watch how the bacteria grow and spread until they reach the next strip.
See how random mutations let new strains survive and expand into the strips with more antibiotics....