One of the most beautiful molecular machines known!
The first one with such complexity that was uncovered.
The ATP synthase complex is so large that Power, Sex, Suicide by Nick Lane (2006) page 123 contains a cryoEM image of several ATP synthases on small membrane vesicles, this is the paper: pubs.acs.org/doi/abs/10.1021/bi00437a031# under a fucking paywall.
ATP synthase in action by HarvardX (2017)
Source. Just like the adenine nucleotide translocator moves ATP/ADP in and out, this one moves loose phosphate in.
Both of those together recycle the cellular respiration carriers from/to the mitochondria.