Secret Sub Levels & What is your dungeon doing here?

These are for quickly adding sub-levels

If you have some needed player absence, a sub-level might be a convenient quick add-on and call it "scouting"

They can be good if the party is not quite ready to go deeper

Some monsters can hide in these if hit by a disaster like murder hobo bullies 
Then repopulate the dungeon later

Maybe more complex need these

Monsters can use some for storage

Maybe i need to write domain rules for running your own dungeon
I have a knack fo making adventurers occupy dungeons

d12 Secret Sub Levels

1 Hidden caverns - a natural cave system older than the dungeon and prehistoric remnants
2 Sewer system - drains and sewers ideal for giant rats and monsters to hide
3 Creepy catacombs - tunnels used for burial niches or an emergency hideout
4 tomb complex - individual tombs or a large tomb or mausoleum
5 Secret temple - religious complex, for secret cult or sealed long ago
6 Mine tunnels - winding passages of a mine still in use or long forgotten
7 Sapper tunnels - enemies tried to invade with their own tunnels and secret rooms
8 escape tunnels - secret passages for elites or others to flee in emergencies in a panic
9 Hidden prison - oubliette or secret torture chambers or cells for VIP
10 Waterways - natural grotto, underground river or lake but possibly a built cistern

11 Monster burrows - monsters have been burrowing around the dungeon 

12 Magical secret lair - a magic monster or person has secret lair possibly secret to the main level

d12 Special Secret Sub Levels

1 Mythical labyrinth - mysterious moving mazes with threats to protect something
2 Dreamland - a ghostly demiplane of delusion and dreams with trapped souls

3 Wrecked star vessel - from beyond the sky alien beings with strange magic

4 Dungeon Dimension - living malicious infinite dungeon invading this realm

5 Inside a rotting god or kaiju corpse - with parasites, undead and scavengers 

6 Inside a living god or kaiju corpse - with parasites and living ecology inside

7 Roots of the world tree - draws from underworld and other regions of the world tree

8 Xor - a living universe of hungry flesh intruding into this world to devour it

9 Faerie beings demiplane - colony of unique ancient fey folk, remnants of the past 

10 Elemental demiplane - elemental cults and beings drawn to a elemental power node

11 Demonic demiplane - demons stockpiling here to support a cult and spread influence
12 Hellgate to 1st plane of hell or one of its demi planes (library, sewers, boiler room)

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This is for those random dungeons on the frontier

d12 What is your dungeon doing here?

1 Refuge for monster peoples driven from other lands and highly resentful
2 Colony of a larger colony an outpost for expansion, espionage or banditry
3 Criminal enterprise often employing or allied to monsters
4 Cult centre for local weird forbidden religion where they can be themselves
5 Private place for unethical research or illegal magic for profit or power

6 Serving the dark lord, aiding their return, espionage and searching for evil relics

7 Millitary outpost for foreign or non-human nation

8 Robber Barron base to raid local region, possibly supported by enemy lands or monsters

9 Warlord plans to carve out own regional power base and conquer

10 Searching ruins for relics and magic for profit and personal power (monster adventurers!)

11 Murder hobos invaded and took over for profit, they fit in better here than towns

12 Charismatic despot inspire others to violent glory for the master's weird needs

Thinking maybe dungeon-maker spells like this:
3rd Lv - hide door, permanent makes a door a secret door blends into a wall

also more spell for traps