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Ok, I read the responses to my last question, and took them into consideration while trying to design my modern era magic-proof underground airbase.

So, we have some mundane methods of control first:

  1. Uber-tight control over things and information leaving the facility, to prevent would-be spies from getting their mits on anything that could be used in spells to track individuals or equipment.
  2. The curved armor that protects the entire underground facility incorporates a 1-foot thick layer of lead.

The magical defenses include:

  1. A Weirdstone at the heart of the facility, protected via a blast-resistant armored casing.
  2. Permanent Forbiddance spells covering every square foot of floorspace.
  3. A permanent Mordenkainen's Private Sanctum protecting each main command and control center.
  4. Permanent Anti-Magic Fields around the perimeter of the bunker.

Perhaps it's a bit extreme, but this is a critical defense facility that has nuclear warheads on site. Overkill is always better then not enough. So, are there any discernible chinks in this place's defense that I failed to notice?

I basically want the only options for getting into this place to be either

  • A: Be let in after being cleared through security.
  • B: Blow the top of the mountain off.
  • C. Ask for help from a god.

The sheer cost of all this would not necessarily be an issue, as this is a government project for the nation's military.

Jazzyamx
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    D&D 5e, at least, doesn't have any official rules for modern technology. Additionally, you should limit this to one system (5e or 3.5e) because the answers will likely be drastically different. – Blake Steel Sep 05 '20 at 05:59
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    @BlakeSteel, I removed most of the tech stuff and 3.5e. Just focusing on 5e magic defense. – Jazzyamx Sep 05 '20 at 07:27
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    @BlakeSteel Yes, it does, but it's UA material aside from the rules for guns in the DMG. https://dnd.wizards.com/articles/unearthed-arcana/modern-magic – nick012000 Sep 05 '20 at 11:10
  • @nick012000, I have been using some of the UA stuff to build the tech/magic interactions. Just narrowed the question to only the magic stuff at Blake's suggestion. If you want to see what I had, look in the edits. – Jazzyamx Sep 05 '20 at 11:18
  • I think the question still needs to be more narrow, for instance, "how is it possible to do X in these circumstances". If the question is as generic as "how secure it is", how do we measure security? – enkryptor Sep 05 '20 at 12:06
  • @enkryptor, I tried to narrow the question--is this better? – Jazzyamx Sep 05 '20 at 12:12
  • That's better. I also suggest removing all the irrelevant parts and describe the attack vector more specifically ("intrusion" is too generic, do you want to prevent destruction, information of being leaked, things stolen, escaping prisoners, etc) – enkryptor Sep 05 '20 at 13:11
  • Also, are PCs supposed to infiltrate the fortress somehow? It it is for NPCs only, just say it is impervious, that's enough. – enkryptor Sep 05 '20 at 13:12
  • @enkryptor, I'm trying to prevent anyone unauthorized from entering the facility. This isn't a game, but a story that I'm writing where D&D magic works. Just thought I'd run it past the folks here to make sure it stood up mechanically. My main character, a young dragon, lives in a decommissioned base, though he has repaired the magic and physical defenses. He's trying to keep well-meaning but unwanted human help out. – Jazzyamx Sep 05 '20 at 21:09
  • Let us continue this discussion in chat. – Jazzyamx Sep 05 '20 at 21:37

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The defenses you describe seem redundant. The Weirdstone (which you'd have to homebrew, I guess) says that it prevents divination magic and planar travel. Then, the "uber-tight control over things and information leaving the facility" makes divination more difficult, the forbiddance prevents all planar travel, and the private sanctum prevents divination magic and planar travel. So you've prevented divination magic twice and planar magic three times.

If you're willing to homebrew the weirdstone, it seems to me that you should just use the weirdstone. If you want redundancy, use two weirdstones.

(Why are we relying on weirdstones? Well, the other effects can be shut off by dispel magic. Someone standing outside the fort could cast dispel magic targeting your forbiddance effect and shut it down, and I believe this would work even if there was an antimagic field in the way.)

If I were trying to gain entry to the facility, I'd probably ambush and mind-control some of the guards when they left the facility for leave. I'd ask them for a detailed description of the contents of the facility. I'd use modify memory to make them forget they'd been mind-controlled -- a careful reading of the spell seems to suggest that an antimagic field wouldn't restore the memories. Once I controlled the guards at the facility gate, I could march the rest of my force right in.

You can counter part of this by using greater restoration on arriving guards, and probably you'd also want to use detect thoughts on them to check for moles. But I don't know of a good way to prevent the thing where someone ambushes a guard who has left the facility and uses mind magic to learn everything they know. If your security policy is that nobody can ever leave the facility for any reason, people aren't going to want to work there.

Dan B
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  • Moreover, comments say the goal is "to prevent anyone unauthorized from entering the facility", so any divination magic can be actually allowed. – enkryptor Sep 06 '20 at 10:59