Hi.  I am adapting the module "A World Gone Mad" (Drivethru Rpg,  Victorious RPG) into 5e for my 5th level party.  Synopsis on the original: Insane asylum with tesla coils to dampen superhero powers.  My 5e idea:  Also in an asylum, but dampening magical powers while traits still exists.  My story synopsis:  This is the last episode of an adventure on Caftenor (Moonshae Isles) before party reaches level 6.  This is a psychological dungeon based on a multitude of horror films and real life events (Think Bedlam Hospital and films like "The Ninth Configuration", "Shock Corridor", and "The Snakepit", set to Alice Cooper's "From the Inside" album) in order to put the players through a series of psychological tests.  The key in this is that one of my players is actually a clinical psychologist...so I am making this as real and as midaevil as possible.  The asylum is run by a Beholder (who will only appear in his lair in caves beneath the asylum outside of this other anti magic field) and a few charmed minion psychiatrists, Doctor Tarr and Professor Fether (Alan Parsons reference).  There are also some clockwork orderlies (warforged?) called "Ratcheds" (nudge, wink) to control the "inmates" (and the players) who are put through various old school things like rotation therapy, morphine treatments, and lobotomies depending on dice rolls.  There are a series of murders in the asylum and the players job is to convince the two doctors that the Beholder is obviously behind the whole plot.  I could get a lot deeper into the story, but that will suffice.  MY QUESTION:  What items can I use to create a large scale anti magic field to affect specific wards of an asylum?  I had considered the idea of somehow using the central eyes of other lesser beholders that have fallen to "The Warden", but I am not sure how to make that work.  Any suggestions would be appreciated.

Your the DM, it can just exist for any reason you want: natural formation of antimagic rocks, a permanent enchantment, a bunch of beholder eyes, some glowing crystals, etc...

The question should really be: what properties do you want the field to have?

E.g. do you want the players to be able to "turn off" the field? If so you need it to originate from one or more objects they can destroy.

Do you want them to be able to turn it off in sections or all/nothing? This determines whether it is one central source object or multiple isolated sources.

Then what narrative purpose do you want it to serve? Do you want it to foreshadow the beholder? Then use beholder eyes. Do you want it associated with a lesser boss - e.g. a mad wizard - then use something more arcana / wizardy.

I like the idea of using Beholder eyes for this because it creates clear counterplay; the Beholder's antimagic field is a cone, and the eye has to be visible from the field it generates. I think if you're going to do large scale antimagic you need to give your players ways to get around it. Blanket bans on casting aren't fun, they just exclude characters who rely on magic from the game.

Quote from Mdhe >>

I like the idea of using Beholder eyes for this because it creates clear counterplay; the Beholder's antimagic field is a cone, and the eye has to be visible from the field it generates. I think if you're going to do large scale antimagic you need to give your players ways to get around it. Blanket bans on casting aren't fun, they just exclude characters who rely on magic from the game.

 
^Came here to say this. You don't want to just shut off the wizard PC.

I feel like I should make an anti-magic dungeon now....