The amount of complexity is just absolutely insane. My favourite example: DNA is read in triplets. So, for example, "CAG" adds one Glutamine to the protein it's building[1].
There are bacteria that have optimised their DNA in such a way that you can start at a one-letter offset, and it encodes a second, completely different, but still functional protein.
I found the single cell to be the most interesting subject. But of course it's a wild ride from top to bottom. The distance from brain to leg is too long, for example, to accurately control motion from "central command". That's why you have rhythm generators in your spine that are modulated from up high (and also by feedback).
Every human sensory organ activates logarithmically: Your eye works with sunlight (half a billion photons/sec) but can detect a single photon. If you manage to build a light sensor with those specs, you'll get a Nobel Prize and probably half of Apple...
As a dancer, I have been fascinated by that fact. It means that dancers do not dance to the beat as they hear it - it takes too much time for the sound to be transformed by the ear/brain into an electrical pulse that reaches your leg. Instead, all dancers have a mental model of the music they dance to that is learnt by practice/repetition.
Dancing is just syncronizing that mental model to the actual rhythm that is heard. When I explained that to a bellydancer friend she finally understood the switch that she had made from being a beginning dancer to an experienced dancer who 'dances in their head'