Ms. Poppins:
Having an ingenious idea, you open your Rainy-Day umbrella, project a forcefield and put it under the fall to see whether it holds up. You struggle for a bit, but it seems it holds up fine. You are up to your armpits in the water, arms upraised to protect you from the immense force of the waterfall precariously above.
Inside the fall is a small cave. Squinting, you find not an entrance, but a very angry looking snake. And a very, very big one at that.
Thruster:
You flip the coin. Heads! You feel really lucky right now. Absurdity points increased to 4! You follow Ms. Poppins, holding up the waterfall with her umbrella, and look behind the fall to examine the cliff face. Still jagged, mossy and dangerous. You feel Ms. Poppins bump into you. Turning her direction, you find a gigantic snake poised to strike.
Doc:
You activate your Shadow XI telepathically and command it to scale the fall and slip into the entrance. You find that the shadow needs a surface for it to travel; it can't fly, and doesn't function in the case where you make no shadow, like in complete darkness. The Shadow XI successfully slips into the circular metal door. Outside the door is what looks like a fingerprint scanner, but it isn't shaped like a human hand...
Inside the Snake Den is a long, long hallway. Too far for it to travel without disconnecting from your control. What looks like mud is strewn throughout the length of the hallway, leaving weird prints.
Worm:
You actually find what seems like another entrance! Though it is impenetrable nonetheless. It is not blockaded by titanium doors, nor a laser tripwire system. It's simply too small. Your hand barely fits there. However, your laptop scans show that it leads into the complex.
Dancer:
You find some trees that look like they can be climbed easily, and a small pathway leading to the top of the waterfall. The tree is precariously tall, though. It seems to be just the right height to reach the entrance behind the waterfall, but it looks like you'd need inhuman dexterity to manage it.