Melbourne

I’m not familiar with the features of this castle but off the top of my head… Probably not. You run out of food and water very quickly under siege, and close proximity with poor sanitation would lead to disease spreading through everybody.

Subsistence farming is slow and hard af. The soil might be contaminated or lack nutrients, and you’d really be relying on good steady yields. Hard rain, pests, diseases or rot could wipe out your crops. You’d want to be companion planting and doing crop rotation and even then there might not be enough space to sustain many people or enough of the right nutrients to survive long term. It’s also heavy labour on not a lot of food.

Zombies tend to be attracted to humans and would pack themselves closely in masses around the perimeter and they don’t need to leave for any reason. Can’t be scared off. Don’t sleep. Pouring down boiling water or oil would only do superficial damage to the undead as it wouldn’t necessarily destroy the brain. All of the precious limited ammo wouldn’t make a dent in hordes. And there’s always more coming.

Could try tunneling out for a supplies route (water, firewood?) but good luck if zombies breach or other opportunistic humans find it. The people would be trapped inside and basically fish in a barrel

Edit: Ohh man I just thought of something. If the zombies packed up against the walls to the point they started trampling and piling up on top of each other (or got killed and piled up) some might be able to climb or walk over. How fucked would that be.

Also no word on whether you might have to keep out zombified scavengers like crows, or whether it can contaminate water or be carried by game/livestock