Deeper Underground… A secret dungeon level. (Patreon)

Below the dungeon level detailed in the adventure is another. A deeper area that can be found if you know where to look – like after you got that treasure map from the Ogre Magi that showed where the secret stairway is, and hinted at a much larger treasure below…

Here the dungeon intrudes on a large natural cavern that has been expanded in a few places with structures cut into the cave walls and then fixed up with masonry. These chambers include some that appear to be religious in context, or at least ritual spaces of some kind (perhaps for arcane rituals of the deep dwellers), but all are secured by sturdy locked doors of which the ones facing onto the cave itself are barred.

The map will lead to one of two chambers containing the treasure. The south “ritual chamber” with tapestries and a set of orbs set into the floor (room 9), or the chamber in the eastern complex that has spyholes overlooking the cave below (12).

The 1200 dpi versions of the map were drawn at a scale of 300 pixels per square and are 9,600 pixels (32 squares) wide. To use this with a VTT you would need to resize the squares to either 70 pixels (for 5′ squares) or 140 pixels (for the recommended 10′ squares) – so resizing it to either 2,240 pixels wide or 4,480 pixels wide, respectively.

https://dysonlogos.blog/2023/02/20/deeper-underground-a-secret-dungeon-level/