Okay, so feel free to edit this.
Do secret rooms exist in the "main world" or only in instances?
I have only found secret rooms in instanced dungeons.
Is there a limit of how many secret rooms that can be generated for each area/instance?
So far, I think I have have found a max of 3 secret rooms in a single floor inside of a dungeon. Those were real secret rooms, not associated with that dungeon (like the broken detonators that require plungers to work etc.)
An instance can have several levels, is there always a secret room for each level?
I haven't found a secret in every level of an instance, but I could have missed them.
How many different types of secret room door-opening-mechanisms are there?
We have found three so far:
- vine bridges extending (instance specific?)
- using a detonator to destroy a rock wall (instance specific?)
- clickable picture-frames or tablets on walls (instance specific?)
What determines the content of a secret room?
I have no idea, but I suspect it's automatically generated somehow.