Cave exploration isn't for the meek. It doesn't take a listen of Gram Parsons' version of "Miller's Cave" to know that caves are far worse than a little claustrophobia — regardless of their size. Speaking of the more sizeable caves, lets talk about the Krubera Cave in Georgia (the one near Russia, not Miller's in the one in the heart of Dixie), which just got mapped in spring of 2014.
Apparently there are still some unexplored regions left on this planet. Still, geologists have known Krubera was the deepest cave in the world since 2001, when adventurers (what else could you call such men?) reached 1,710 meters and still couldn't find its terminus. In case you're curious (and of course you are), they still haven't found the bottom, but have now extended the cave's mapping to a staggering depth of 2,197 meters, which required diving equipment. This recent expedition landed Krubera on an exclusive list as the only cave in the world deeper than 2,000 meters. For those of you keeping score, that's nearly a mile and a half, and just under seven Eiffel Towers.
While spelunking is often far from simple, descending this network of underground tunnels is on an entirely different level of caving complexity. Think of it more like climbing a mountain, but in reverse. Expeditions require multiple days of logitistics, with explorers making camps along the way to keep going. When you're heading down that deep, you're going to have to hunker down under a tent to keep warm, because apparently getting close the core of the earth doesn't make you any hotter. What's more, explorers of the cave need to use dye as a way to leave a trail of breadcrumbs leading back from whence they came. Descending the cave often happens in shifts of up to 20 hours.
It's not just the sheer depth of the Krubera Cave that makes it amazing, nor the fact that human beings have yet to fully explore it. The limestone that makes up the cave is more or less as old as the dinosaurs, and each expedition is yielding the discovery of new life forms along the way. No word on whether or not there are any frost giants or other unspeakable Lovecraftian horrors lurking within.