While not required to visit, the Tatalian Abyss does offer new items for you to gather. There isn’t anything on the first level, so head northwest and jump down to B1F.

The north half of this level has two treasure, 800 Gald in the northeast corner and Copper Ore x2 in the northwest corner. The south half also has a treasure by taking the east path to the ladder, where the Weird Fragment can be found in a chest before jumping down.

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There is plenty of treasure on the B1F to get, so make sure to grab them even though this area is optional.

Unfortunately the lower floors do not contain any treasures, so you might as well head back up and continue to the Dimensional Breach.