The most full of spiders.
This word makes people think of places with many spiders, which can be scary for some people.
Examples:
The old house is the spideriest place I've ever seen.
The basement is the spideriest part of the house.
The spideriest room in the house is the attic.
I don't want to go in there, it's the spideriest place ever!
The forest is the spideriest place in the whole world!
The spideriest room in the house is where we keep the old things.