It is said that dragons roam the caves below the block we know as the Minecraft world. A theory is passed about saying that very, VERY few people have seen one... and lived. And even fewer have managed to escape to the surface. IT is also said that when you dig deep for diamonds, you can hear the faint screams of those slain, stolen, or eaten by such beasts. Which is why, if I manage to load my map to multiplayer access, I will post a sign for when you use my main cave for deep underground access.

Do be careful... The main worry I would have... is always, the Creeper.