Some cool things people can do
with the right resources, 
and a lot of practice.

In Building Your Brain episode 3, BBC covers the Moken people who train as children to see clearly underwater.  See clip of episode here, and find full episode here

Wim Hof, the Ice Man, can swim in icy waters that would kill most people. 

Terence Tao photo attributed to: http://www.ipam.ucla.edu/news/royal-medal-awarded-ucla-professor/

At age two, Terence was teaching five-year-olds how to add and spell. He went on to work with Ben Green on the Green-Tao theorem about arithmetic progressions