Childbirth. Just the physical volumes involved are impressive, especially with that dummy big head that has to flatten out, but there's also calculations showing that in the later stages, the mother is actually using energy at the fastest possible rate the human body can sustain for more than a short burst.

On that note, eating. You can just take in certain random things from the environment, and your body can rearrange it partially into more body and partially into energy. No artificial machine I'm aware of can do that.

Living outside of water. Life is a water thing, it started in water and cells are mostly made of water. We can just kind of bring our own supply, and that's crazy. In a lot of ways your house is more like outer space than the place where we started off, and indeed the human body can tolerate a total vacuum for a bit without damage.