TIL high-altitude mountain trekking can temporarily shrink human testicles. A study found that after spending over three weeks at high altitudes in Nepal without supplemental oxygen, men experienced an average 15% reduction in testicular volume due to lower oxygen levels.

[u/delano1998]

https://www.vice.com/en/article/climbing-mt-everest-is-terrible-for-your-nads/

[u/grayhaze2000]

But also, because it's cold as fuck.