You already mentioned cult-like behavior, so isn't religion is already a good go-to for creating a sense of purpose?

A slightly bigger scale, but worth reading (really): goodreads.com/en/book/show/12287209-wool

You might read up on the (now destroyed) Kowloon Walled City. While not technically a bunker city, it certainly meets lots of the criteria otherwise.

Why no electricity?

I wonder what they used to do in cloistered nunneries? Or maximum security prisons?

Did you mean incest or inbreeding?

No access to sunlight is a big problem, as is the related problem of vitamin deficiencies.

How are they getting access to food, heat, and water without any ability to go outside and no electricity? You need a substantial amount of farming land to feed that many people, those farms need water and sunlight. You also need a substantial amount of fuel to provide light and (more importantly) heat, for which wood is the obvious source but also needs sunlight and water.

the incest vs inbreeding was a translation mistake I made :) but honestly.... I fear there could be little of both if unsupervised. As for the nunnery comment - I actually grew up in a town with a nunnery. The nuns were somewhat famous for building skeletons with gold and decor, one of them embroidered a cloth for 10 years until she went blind. As for the mother superior? She's a broker for the church :D a mad one indeed

Didn't approximately the entire planet basically do this in 2020? How did we survive...

@GregBurghardt We had internet and food delivery :P

There is no way this can be told as anything but a horror story. This is 10 Cloverfield Lane, and Vanishing on 7th Street, and A Quiet Place, and Love and Monsters. You can say "but they can play games" all you want, they die if they attempt freedom. Your prison guards are predatory creatures instead of uniformed officers. This is a prison, and the answer is a horror story, not a worldbuilding problem.

Why do they not have solar panels, wind turbines, generators to provide them with electricity and entertainment. Modern TV can be 50w and with a few batteries a TV can run ages on a single charge. If there near a stream maybe they can even have hydro power. Keeping these things maintained will surely keep a percent of your population occupied.

@VogonPoet unless you give them internet and electricity. Now it becomes a comedy of a bunch of shut-ins watching anime and manga and writing fanfictions for life. For quite a bit of us, it is the dream life--esp if you have the ability to make new anime, manga, and games

@FaitoDayo I have spent entire weekends playing Zork or D&D without sleep. I get that. But even that has its limits I think.

@VogonPoet it is because you just play the same game over and over. But we are talking about watching all animes and manga and play all games. This is an astronomical number of works that you can enjoy.

How do you know we haven't already gone crazy. 😜