Cliff
There is a mountain on top of a bunch of dirt with a steep cliff. This is a bit redundant, but the mountain and the dirt just make the cliff even bigger and steeper and scarier.
Imagine a cliff. Now add two big helpings of dirt and a mountain to the top. It's still a cliff, it's just more cliff than before.
がい
がけ
None
You can't believe how big the cliff is now with the mountain and the dirt. You look at it for so long, you just become another gawker (がけ) who can't stop staring at the huge cliff. It really is huge.
Imagine a giant cliff that turns every passerby into a gawker, just like you.