If you ever visit Slovenia and ask the locals about Mount Triglav, some of them will tell how their folklore has passed down the belief that inhuman creatures live in caverns there.
Then you may be tempted to explore more, and even go to see the mountain itself, looking for any entrances to some sort of cavern. Perhaps you will find one and enter it.
You might not be prepared for such an expedition, but you will go on nevertheless. The cave may go on for a long while and you may reach what seems to be massive pool of water. Perhaps you will step into, and perhaps you will be swept away by a sudden and unnatural current. You will no doubt panic at this point as you are pulled into subterranean waters.
Your breath will run out and the world will go black. And then you will feel soft, webbed hands gripping your body. Perhaps you will open your eyes in shock and witness a mass of long, white snakelike bodies around you. You might even see their webbed hand and feet, and maybe even their reptilian faces with massive monotonous silver eyes and purple external gills that extent like fans from their necks. You will no doubt wish to escape by now, or perhaps you'll disbelieve this.
Sooner or later your consciousness will once again fade. And then you will wake up, but you are no longer in the nightmarish realm. You will shrug it off as a hallucination, a bout of madness, a dream. But you can't forget it. Ordinary things will seem to take new meanings. Especially symbolic things. Crosses, deer, mountains, seashells, these are only a few of the countless amounts of hidden meanings you'll find. When you see one you will have to tell yourself to stop staring, stop listening to hidden messages mere images can whisper.
You will notice you can predict some of the coming events. First they will be incomprehensible prophetic dreams. Then you can see flashes of what's to come in broad daylight. Finally you will learn how to control these abilities. You can become rich, powerful and famous this way, and you will know there are people who have used these abilities to do so. But every time you peek to future you will also feel the ever strenghtening call of the caves. You will feel the hands on your body again. The symbols will become more and more of an obsession. Unless you know when to stop, this will consume you and you will do everything you can to return to the cave... I don't know what happens afterwards.