The Mah’habara Subterra is completed during Chapter 11. The story takes the characters through this zone after they reach the Archylte Steppes but, after passing through the Mah’habara Subterra and reaching the Sulyya Springs, there are a few optional zones that you can reach if you go back to this zone.
All you have to do to reach the optional areas is to travel back to the end of the Mah’habara Subterra where your team jumped on Atomos and rode the fal’Cie to the Sulyya Springs. There is a new zone that can be reached by simply jumping over Atomos and using him as a bridge.
The easiest way to get there is to use a Waystone and choose to teleport to “Sulyya Springs - Ceiling of Sky”. Once you have arrived, turn around and approach Atomos (marked as a big pink splotch on the mini-map) and press the 
Button to board.
When Atomos arrives back in Mah’habara Subterra it will place you on the proper side already facing the newly available optional zones (“An Asylum from Light” and “Abandoned Dig”). If you turn around though you will see that you can jump across Atomos to reach both sides, and you can choose to board Atomos to return to the Sulyya Springs if you choose.
There are quite a few Treasure Spheres available in the Mah’habara Subterra optional zones but none of them are exciting enough to warrant traveling to these locations on their own. Besides that, you will naturally be able to pick up all of the items as you venture to this area for the its two primary purposes which are:
Starting in the Twilight Cavern, where Atomos drops your party off, venture forward and you will reach a 
Save Stations where you can save your game. Keep following the pathway which now has you entering the “An Asylum from Light” area of the map. You will have to battle a group of two Yakshas.
The path will actually split just after this, though it isn’t immediately obvious. The pathway on the right requires you to jump across a small cliff towards a Yaksha and Yakshini pair.
Keep following this walkway until you see a set off stairs on the right side of the cliff that leads down to a Treasure Sphere that contains a 
Moogle Puppet. As a reminder, these Moogle Puppets can be sold for Gil (it's their only purpose).
Continue down the trail to the next group of two Yakshas with a Yakshini and after that you will reach a fork in the road. You’ve now reached the “Abandoned Dig” area of the optional zones; regarding the fork in the road though, it doesn’t really matter which side you take.
You will come across a new enemy called a Strigoi in this area which is very easy to defeat. At the end of both pathways is a Treasure Sphere that contains a nugget of 
Perovskite.
Keep following the trail to find yet another Vetala. These enemies should be getting easier and easier to defeat as your party continues to gain power. Ideally you are able to defeat them by Staggering them just once without them being able to reapply “Inertial Barrier”. The last group of enemies just up ahead includes two Strigois.
Use the Save Stations just up ahead and then move forward when you’re ready to engage the mark. Note that tactics for completing Mission 30 are available on the Mission page linked below, although the fight itself is fairly straightforward:
Don’t forget to grab both of the two Treasure Spheres before leaving the area. One of them contains four Perfect Conductors while the second contains two Particle Accelerators.
After completing Mission 30, your next Mission, Mission 31 - Newfound Purpose, takes place in the newly opened area behind the Cie’th Stone Paling that has just opened. In other words, you’ve got to head all the way back out of the Mah’habara Subterra. The other branch of the optional zone leads to the Cie’th Stone for Mission 53 - Freedom from Fear which technically is available now, but this can be completed later on.
Use the link below to return to the Chapter 11 Optional Side Quests page if you came here from that section of the guide:
In addition to the Cie’th Stone for Mission 53, note that you can find the following Treasure Spheres in the other sections of “An Asylum from Light”:
Perfect Conductor (x3)
Rainbow AnkletMetal Armband (x2)Particle Accelerators (x2)
