If you’re into true-adventure sea-faring yarns you can’t go wrong with “Shadow Divers,” a story about hard-core divers who found a sunken German U-boat off the coast of New Jersey.

The book’s a couple years old — somebody at work gave me his copy and said “Tom, you’re into outdoors stuff, you should like it.” I read most of it in one sitting; it has that same “Into Thin Air” breathlessness of purpose and prose that ends in sore eyes and lost sleep from curling up on the couch into the wee hours. But it ends well, with the satisfaction of having been taken along for an amazing ride with some of the gutsiest outdoorspeople on the planet.

Why write about ’em on a hiking blog? It’s not like we’re into death-defying forays into the hazy depths. We do sane stuff, like stay on trails and leave no trace. Deep-wreck divers leave traces. They knowingly and willfully wander through undersea graveyards where a single snag of wreckage could land them among the ranks of the lost at sea. Books like “Shadow Divers” make much of the bravery, determination, obsession and madness that are the grist of great drama, but they’re also instructive about why otherwise ordinary people can pull off amazing feats.

Mainly, they do it because they know how. The stars of “Shadow Divers” taught themselves to deal with incredible physical adversity to dive below 200 feet, where a condition called narcosis made them essentially half-drunk in an impossibly dangerous setting in which panic snowballs into an underwater drowning or a surface case of the bends, in which large bubbles of nitrogen can form in all sorts of inappropriate locations, like essential bodily organs. (The book describes three of the shadow divers perishing, one by drowning and the other two by panic and failure to decompress).

The question is always “why do they do it?” And the answer, as far as I’m concerned, is very simple. Because they can. Why can they? Training.

Sure, this oversimplifies, but it helps me demystify the business of doing remarkable things.

For people who’ve never done it before, a five-mile walk in the woods might seem as imposing as diving 200 feet into the ocean to explore a shipwreck. Lots of dangers in the woods: wild animals, falling rocks, deep ravines, potential for getting lost, potential for never being found. Each hike tells us a little bit more about how to make sure we’re around for further outings.

Live and learn, as the saying goes. Or learn and live.