Dungeon Durability

INTRO

 In the late 2000s and early 2010s there was a small obsession in video games with "fully destructible terrain." Wooden cover would splinter in Mafia II, the sides of buildings could be blow through in Battlefield 3 and pretty much everything could be blown up in interesting or advantageous ways in the (still remarkably ambitious) Red Faction: Guerilla. To put it simply, this shit fucked.

Tabletop Games (in my experience) don't share this obsession with this full destructibility, especially in terms of mechanics, instead shifting that responsibility to the GM. While we can (and have) knocked out walls in our OSE campaign there's remarkably little consequence for this besides making some noise. What few games do mechanize this environmental destruction often get so granular as to be unapproachable (with Cyberpunk 2020 toeing this line to mixed effect).

My reading backlog's pretty thick right now, so maybe someone somewhere is already doing this, but after reading Catching Snakes' Dungeon Immune Responses, it got me thinking back to how I was going to handle a Space Hulk[*1] and its own dungeon durability...

THE GIST

The walls of the dungeon are thick, but not impenetrable. Magic missiles blast through them with ease, and one wrong swing from an adventurer's war hammer may bring a support beam crumbling down. Each area of the dungeon has a set durability (let's say d6+2 durability for the average catacomb), and each section of dungeon wall, ceiling and floor can be easily broken through by dealing 1HD of damage in a single strike.

Each time a section of wall is destroyed, a door is broken down or a sufficiently large or earth shaking explosion happens that area suffers 1 Durability Damage, and immediately rolls on the Decay Table - See Below. [[For folks using Hazard Dies or some similar procedure at home, you may also want to weave the Decay Table into that!]] When an area reaches 0 Durability it begins to collapse (or flood, or depressurize, etc). Players have 2d6 Rounds to evacuate before this collapse will kill them outright. After a collapse happens only a few scant hallways of the area are accessible (usually enough to connect adjoining areas if necessary for game flow), the rest has been left in ruin and must be excavated at great cost.

THE DECAY TABLE

When rolling on the Decay Table roll 1d12 and add the area's current Durability. You may want to customize this table to better reflect the dungeon players are exploring!

1. No Escape - Whatever entrance to this area the party used has now completely collapsed. Your only hope is to venture deeper... 
2. The Ground Shifts... The floor of this room crumbles at your feet, you have 1d4 rounds to react.
3. The Snapping of Support Beams... The ceiling in this room begins to collapse, you have 1d4 rounds to react! 
4. Choked By Dust... The air feels far thicker and hazier, dust once grey dances between green and black in the torch light. All actions in this room are rolled at disadvantage. [[After one round all Players must make a Save vs Poison, all feel the urge to cough, those who fail begin coughing profusely, bringing more "dust" into their lungs. If players remain in this room for another 2d2 rounds they expose themselves to Deep Mold, permanently reducing their Maximum HP by 1 for each further round spent in the room.]]
5. Nightmares... The dungeon wails in the dark. The next time you sleep it'll be for 6 hours, nothing can wake you in this time save for losing HP. You'll have a nightmare of being trapped in this very area of the dungeon, looping endlessly. Lose all the benefits of that rest and will feel exhausted when you awake.
6. Emaciated Predator... A fearsome beast from far deeper in the dungeon has been displaced due to your actions... and it's especially hungry now.
7. The Rush of Water... A few bricks come loose in a nearby wall and are now pouring water (or perhaps mud or some other foul liquid) into this room. [[Flip a coin to see if it's enough to flood this room, if it is flip another to see if it's enough to flood this area.]]
8. Chain Reaction... If this Decay was rolled due to the destruction of a structure, d8 nearby or attached structures also fall apart. If no structure was destroyed, a nearby wall finally gives out and crumbles.
9. Chain Reaction... If this Decay was rolled due to the destruction of a structure, d8 nearby or attached structures also fall apart. If no structure was destroyed, a nearby wall finally gives out and crumbles.
10. Something Feels Different... But you can't pin what. [[Swap the locations of two keyed rooms]]
11. Neither Sun nor Stars... Without any way to exactly tell the time, time itself seems to fly by. [[Advance time by d12 hours without the Players realizing, disregarding any associated encounter rules from the passage of time.]]
12. Bad Bones... You can tell the walls of this room will give at any minute. A single point of damage to any wall will not only cause the wall to collapse, but will cause the ceiling to fall in d8 rounds.
13. The Dungeon Quakes... Save vs Paralysis or fall prone as the dungeon rumbles. 
14. The Dungeon Quakes... Save vs Paralysis or fall prone as the dungeon rumbles. 
15. Whispers in the Dark... Save vs Spells, on failure they whisper to you a rumor of this area.
16. Whispers in the Dark... Save vs Spells, on failure they whisper to you a rumor of this area.
17. A Gust of Wind... Some shift from the area's exit causes a gust of wind to come through. All torches are blown out.
18. Screams in the Dark... A crumble, a snap and then a blood curdling scream. Who or what could have caused it?
19. Deathly quiet... Only your footsteps and heartbeat can be heard in this crumbling halls.
20. Deathly quiet... Only your footsteps and heartbeat can be heard in this crumbling halls.

[*1 : For non-Warhammer nerds, Space Hulks are one of the coolest parts of the 40k settings. Derelict spaceships that have been lost to the daemonic warp. Ships out of time, and infected with all kinds of bizarre ailments. Treasure troves waiting to be looted or purged. They're super fucking cool and the tie-in board game continues to be the white-whale of my collection.]