Slugterra's Cavern Systems
It will always baffle me when people say that the 99 Caverns are the 'central caverns' with there being the Eastern, Northern, Southern and Western cavern systems or that the 99 Caverns means there's 99 Infurnus slugs....
There's clear evidence in the series to support there actually being SIX Slugterra cavern systems and that the 99 Caverns is not the 'central caverns'.
Let's address the location of the 99 Caverns. We know that the 99 Caverns is underneath a place that commonly uses the imperil system of measurement (ie inches, feet, yards etc). And given it snows during Christmas, we can assume the country/continent over the top of the 99 Caverns is the USA/North America.
As for the count of the potential cavern systems, we go to Gateway Cavern and the Gateway Portal. The portal is made up of two rings; the outer which indicates which cavern system we're in (picture below is of the 99 Caverns symbol)
and the inner turn-able ring that shows six different symbols. (the sixth is obscured by the steps in front of it) Said ring will show which cavern system you're going to.
I think people forget to count the sixth symbol on the inner ring since they only see five. Or that they count one of the six as the Deep Caverns whilst the sun represents the Burning World/Surface
We know that there's one for the Eastern Caverns (below)
And that the sun symbol is associated with the Dark Bane or perhaps was meant to be a quick way back to the surface,
As for the other four; we have zero idea of which caverns they lead to
Personal headcanons of mine set them as the Southern, Pacific, European and Southwestern Caverns respectfully.
But now lets look at why the 99 Caverns is NOT the central caverns. Just because the 99 Caverns is canonically the largest and main cavern system we've seen/been in for the series doesn't mean it sits as the middle. Bullseye Cavern is the middle of the 99 Caverns, what the residents of that cavern system believed to be the center of Slugterra since they did not know of the other systems TILL the Goon and co attacked.
With the 99 Caverns under America, why would the Eastern Caverns still be referred as the Eastern Caverns when the closest path to them is from the west? Well that comes back down into world geography history! America is referred to as the West and Asia is referred to the East due to England and the UK being the center of attention. So by 'technicalities' under the UK's own classifications, they'd be the central caverns. Though, I don't think there should be 'central caverns', rather Western (99/under North America), Eastern (under Asia), Northern (European/under Europe), Southeastern (Pacific/under Australia & the surrounding islands)), Southern (under Africa) and Southwestern (under South America)
A very rushed map of an example;
Edit: Completely forgot to mention the Infurnus stuff- so quickly adding that!
There is only 2 known Infurnus slugs; Burpy and Joo-Joo. The idea of a Infurnus being the "defender's slug" of the cavern system. It is only true to Eastern Caverns with Joo-Joo being a slug held in Junjie's family for 2000 years.
There has to be at least a few more Infurnus slugs about, but very much limited in rarity (ie, almost One of a Kind per system)












