Lukina Jama, from the Croation Speleology Server. Click through for full size.
At the bottom there is a system of ponds that houses one of the largest colonies of subterranean leeches. Now, what exactly are those leeches feeding on (apart from lost explorers)?
The trogolobitic leech, Croatobranchus mestrovi.
Second, Velebita. This has the longest single vertical drop – 516m. I love that this map seems to have included diagrams of where the ropes go, and pictures of trees and boulders at the surface. Are they like markers to help you find the place: “it’s easy to spot, there’s a big fir tree there and a rock that looks like Groucho Marx’s nose – you can’t miss it”.
Small sample from the Velebita map, again from the Croation Speleology Server. Click through for full size.
These caves, and several others, are all clustered around the one location in the Sjeverni Velebit national park. This cross-section shows just how close they are to each other – shades of the Caves of Chaos?