> Inspect FIERY BLONDE'S COLDWATER BOOTIES

You examine the puddle. It would appear that it was frozen recently. Looking at the direction of the grass leaves, you can deduct that a large object was pushed from this spot into the gateway.
>Kick the gateway.
Break into gate with your awesome halckemy skills.
> Randomly chance upon how to make that gate open for you.

Upon kicking the gateway, a panel pops off the front of it. It seems to be full of GOLD WIRES and MAGIC RELAYS. It would seem that this gateway can be activated using electricity.
>Break down the gate into alchemy regents like Bismuth, Quicksilver, Mythril, stuff like that.
The gate is receiving magic at a constant and steady rate. The magic input disables the ability to break the gate down into it's elements.
Fill the inside of the gate with stone from the cliff behind. Nothing can possibly go wrong with that plan.

Ha. You are such a jerk. Screw magic.
>Spot some obscenities floating down the river.
While you don't find and obscenities floating in the water (if that is even possible), you do find a strange red exclamation mark shaped item.
The dot on the exclamation mark seems to follow the long part perfectly. You cannot understand how it does this. Maybe it has a magnetic field? Or maybe its magic. Regardless, you stash it into your inventory.
A large bang echos from the waterfall, along with the sound of rocks collapsing and falling into the water.

forget MAGIC.