Beholder Under a City: Questions

[Glenn_Beckett]

I’m gonna run a city for my players that has a Beholder hiding out in the sewers, slowly attempting to gather servants until he can dominate/destroy the human settlement. My players might pursue that narrative, and they might not, but if they do, what might this Beholder have done to the sewers to stave off any adventurer stupid enough to come their way (while still allowing servants to come receive instructions)?

[JackPhoenix]

Get the servants a specific place to meet the beholder for instruction. That's NOT the beholder's lair, though: that's in a crazy labyrinth of tunnels he made with his disintegration ray much deeper under the city, full of traps and next to impossible to navigate for someone without flying. The tunnels may hold other, more reliable minions.

[Glenn_Beckett]

Get the servants a specific place to meet the beholder for instruction. That's NOT the beholder's lair, though: that's in a crazy labyrinth of tunnels he made with his disintegration ray much deeper under the city, full of traps and next to impossible to navigate for someone without flying. The tunnels may hold other, more reliable minions.

Yeah, I’m figuring he’s got a ****load of flameskulls down there. Mages who were loyal enough to be turned into something a little more...aesthetic.

[Galithar]

Beholders are paranoid. I would expect some misleading illusions. Basically an illusion that someone would THINK might be an entrance to something bigger (like the beholders lair if they are aware of it) but actually leads to nothing but traps.

The previously mentioned "neutral meeting place" for the servants could/should be similarly concealed so someone can't accidently report to the beholder for orders :P or just be so overwhelmingly inconspicuous that it's literally just '500 feet down this tunnel stop and the voice of the master will be heard' where the Beholder could have a narrow tunnel dug that only had a 1 foot or less opening at the end. Enough he can speak through, but virtually nothing could follow him through it

[Nifft]

It'd be cool to see a lair so vast and disintegrated passages so pervasive that an area of the city started to collapse.

Of course, after each collapse the Beholder moves its lair.

[Tvtyrant]

I’m gonna run a city for my players that has a Beholder hiding out in the sewers, slowly attempting to gather servants until he can dominate/destroy the human settlement. My players might pursue that narrative, and they might not, but if they do, what might this Beholder have done to the sewers to stave off any adventurer stupid enough to come their way (while still allowing servants to come receive instructions)?

Makes a series of vertical shafts a mile deep only he or a vampire could fly through.

Have portions of the tunnels be under a lake or river with only a thin section left, he floods the passages as he flees.

Portions dug around columns that can be collapsed at a single shot.

Tunnels that look inviting but lead to nests of things. Kruthiks, Kythons, giant ants, carrion crawlers, etc.

Ropers planted strategically so the only spot out of reach is a tiny ledge along the ceiling, party has to fight them to pass.

Lake caverns full of water monsters that it just flies over.

Pit traps. So many pit traps.

Gas spores just littering the cave system.