This is 99% invisible.
I'm Roman Mars.
In a valley in central Slovenia,
there's a giant limestone cave called Pel, which means hell in Slovene.
If you look hard at the rocks.
Above the entrance, you can just make.
Out the shape of the devil, which.
Is one explanation of how the cave got its name.
That is British expat and 99pi's Slovenia correspondent, will Aspinall.
I recently met up with Andrej Kappler from the Slovenian National Institute of Biology.
Andre studies the ecology of caves, and today he is taking me spelunking.
I'm not naturally inclined to go into caves.
Is it safe?
It's completely safe.
But there's one caveat in this case, because it was very,
very rainy these days and hopefully it didn't flood.
But if it did flood, then we're in trouble.
Okay, we're in the cave.
The cave is narrow, only about a meter wide in places, but it's like 15 meters high.
It's a chasm and it's flooded.