Let me start of by telling you that if you're going to be questing for the teleport scrolls... be prepared for death. Or beg some high level friends to go protect you. I know the maps for most of these zones are 3K a piece at Jeuno, but it's well worth it.
You'll be coming back here, after all.
A word of warning about Garlaige itself -- mind the holes. Holes = death. If you are unfortunate and fall down by mistake, warp out of there or prepare for a swift beating. I've "seen" a level 33 MNK Elvaan with 700 HP get slaughtered in 3 hits. Baaaaaaad places.
The first time my friend and I tried this mission we ended up both dying when Sneak/Invis ran out and all sorts of fun things aggro'd. There are bombs and pot-family mobs near enough as well, and they're much more unfriendly than the bats and beetles. For those that don't know, undead aggro when your HP is less than 75%; in other words, in the yellow. They will see you through sneak/inivisble. It'd suck to figure that out by getting killed.
Okay, onto the actual quest.
The best directions, and the ones that ended up leading my friend and I where we needed to go were the ones posted by Jyneefur. To repeat -- throw up sneak/invisible when you get to the bottom of the stairs (unless there's a mob train). Make the first left, the first right, and another left. Mind the holes again, I wasn't prepared for them and almost fell down one. The first left you make will be a very precarious path.
For those of you doing this quest in pairs, or randomly doing the quest when another WHM is doing the quest, be prepared for the ??? to move. It doesn't go far; it simply swaps rooms. If you see the ??? but it's out of range, you have to essentially go to the other side. I can't think of concise way to explain it, but if it happens to you, you'll know what I mean.
[_ rm2 _][_ rm1 _]
RM1 is the room that the directions lead you to, RM2 is the room that's directly "behind it". You'll have to go around a wall to get to RM2 from RM1, but it's really not that far.
It's worth the CP to buy a scroll of warp, or just warp out of there with the spell. Not as absolutely necessary as Gusgen, but the sooner you get out of there the better.
ALSO! Yet another clarification!
When you go back to Bastok to talk to the starter NPC Virnage, he will tell you that he DOESN'T HAVE ANYTHING FOR YOU. He gives you a Key Item, "Letter to Eperdur" and you must return to San d'Oria and go to the Cathedral in N. Sandy to get the scroll.
I'd also like to confirm Vanex's cabbage fame building guide. It took me roughly the same amount of cabbages to get the required fame (I could hold more stacks, having done Gobbiebag I, that helped a bit). This is a very time consuming thing as simple as it sounds, so be prepared to spend all day and a good chunk of gil raising your fame in this manner.
I hope this helps someone else in the future ^^ I'm just so happy I got it over with.
...now to do Mea. Ugh.