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After finishing the FIRST floor of this damn dungeon, we continued after taking a quick break of half an hour.
Each floor was simply an extension of this biome, and they were connected by a single staircase that led downwards, when you reached the next floor, the stairs were still there, resembling a tower that connected with the sky, quite bizarre.
There were no particular changes in the environment of the dungeon nor any of that, although there were things such as lakes and rivers too, which sometimes came with surprises such as giant Catfishes, all of the Rank 3, mind you, and deadly Thunder Eels, also Rank 3. They were interesting monsters that zapped me a lot, but I caught them and killed them. Eating them roasted was advised, with a lot of sweet sauce, but we saved them for later.
Check "The Protagnist's Sister Is Actually the Strongest"!