Meet Wim Hoff. He set the world record for longest ice bath and climbed Mt Everest in his skivvies. He's not just a daredevil, though. He's out to prove that cold therapy has real health benefits... and it looks like the science is starting to back him up.
You don't have to sit in ice water for an hour like Wim to get the benefits. Regular cold plunges of 30 seconds or more will improve circulation, reduce inflammation, and boost immunity. There also appears to be an endorphin response which works as a natural anti-depressant. In the past, humans had to endure periods of extreme cold, so it makes sense that our bodies would have developed positive adaptations to it.
If you don't happen to live near an Icelandic stream, you can do what I do. Take cold showers. Yes, the first time will put an OMG expression on your face, but after a few moments your blood vessels will relax, and you'll start to feel invigorated. As Wim says (in his Dutch accent), "The cold will become as comforting as a pair of flannel pajamas". I repeat these words (with the Dutch accent) every morning before stepping into the shower. Hey, you gotta psyche yourself up!