There are two secret rooms that we found in the Catacombs in ATLYSS. You can find the locations of the secret rooms in this guide.
ATLYSS Catacombs
Here is the location of the secret rooms of the catacombs:
Locations
Bridge Room
Look here and jump into the darkness.
You will find an extra key!
Lower Bar Room
Same as the last room! use the pillars to jump into the darkness.
You will find extra pots and chests in here!