Wim Hof Method.
   This is a recreational practice followed by thousands of people for
   being comfortable in extreme cold.

   Week 1: 30 seconds of cold shower after a warm shower, for one week.
   If I miss days, I can maybe modify the protocol to 10 days
   nonconsecutive.
   We'll just see how it goes. In week 2 you upgrade to 1 minute of cold
   water.