spelunk: to explore caves, especially as a hobby
Spelunkers are like ocean explorers or space travelers. They are venturing into places in our universe where other people have never been, and those places can be mighty dangerous. The thrill of the journey and the beauty of the environment are intense and make the risks worthwhile for those who boldly go forth.
Much planning goes into cave exploration, and some of these explorers pull double duty by making maps of their travels. The mapping is actually very mathematical. Much like the surveyors we see out by the sides of roads, a cave surveyor must use trigonometry to accurately mark where they have been and where they are going. Yup, that course whose title literally means “triangle measure” is the heart of the work. You don’t believe me? Ask these guys.