"Neurons in an expanded mouse brain" (3rd place) is also stunning:

https://www.nikonsmallworld.com/galleries/2026-photomicrogra...

I didn't know brains actually look like this inside. Our world truly is beautiful, across all scales!

i'm not an expert but i think the word expansion here is referring to techniques they use to spread everything out in order to make it easier to see. someone told me that they use the same material that baby diapers are made out of which expands when you soak it in water.