Microclimate and other phenomenons in a ludicrously big room

[Yora]

I got this idea for a game, which is to have an absurdly large dungeon that is more or less just a single room. The layout is similar to the Hagia Sophia in Istanbul, but scaled up to the size of the Vehicle Assembly Building of NASA.
The floorplan I have created is close to a 3x3 square grid, where the four corner squares and the central square are solid rock, and the four remaining squares being 90x90x120 meter spaces that are connected where their corners are touching. The outside walls of these four squares are open to the outside with three 20x100 meter archways. To make the whole thing more fun, there are lots of wooden platforms and bridges running between the walls.

If the whole thing is carved out of a solid mountain and the ceilings carved into proper vaults, it might potentially even be structurally sound, though that aspect isn't important here. If it isn't, then the whole thing is just magic. I gladly handwave that.

But the internal space is so absurdly big, that it got me wondering what weird things air circulation and moisture in such a place would be like?

Assuming that the four squares are oriented in the compas direction, the north area would get no direct sunlight, while the south section would get a lot. This should already make quite a difference. Perhaps lots of vegetation on the ground in the south and fungus growth in the north?

But is anyone here good with air circulation? Would the warmer space in the south and the cooler space in the north cause a natural draft, even when no wind is blowing? Any other fun oddities that giant rooms have to deal with?

[Knaight]

There are some layout maps for the Biosphere 2 project you might want to look at here - they could be helpful. Otherwise, given a sufficiently large room you absolutely could get microclimates. Wind is part of that, susceptibility to outside heat another, water a really big third. The room you're describing really isn't sufficiently large though.

[Yanagi]

I got this idea for a game, which is to have an absurdly large dungeon that is more or less just a single room. The layout is similar to the Hagia Sophia in Istanbul, but scaled up to the size of the Vehicle Assembly Building of NASA.
The floorplan I have created is close to a 3x3 square grid, where the four corner squares and the central square are solid rock, and the four remaining squares being 90x90x120 meter spaces that are connected where their corners are touching. The outside walls of these four squares are open to the outside with three 20x100 meter archways. To make the whole thing more fun, there are lots of wooden platforms and bridges running between the walls.

If the whole thing is carved out of a solid mountain and the ceilings carved into proper vaults, it might potentially even be structurally sound, though that aspect isn't important here. If it isn't, then the whole thing is just magic. I gladly handwave that.

But the internal space is so absurdly big, that it got me wondering what weird things air circulation and moisture in such a place would be like?

Assuming that the four squares are oriented in the compas direction, the north area would get no direct sunlight, while the south section would get a lot. This should already make quite a difference. Perhaps lots of vegetation on the ground in the south and fungus growth in the north?

But is anyone here good with air circulation? Would the warmer space in the south and the cooler space in the north cause a natural draft, even when no wind is blowing? Any other fun oddities that giant rooms have to deal with?

Is the exterior carved as well or is it just a mountain on the outside?

The building would experience the stack effect (https://en.wikipedia.org/wiki/Stack_effect).

Air circulation will depend on venting in the manifold...anyplace there's a gap for air to enter or exit. In a giant cathedral (barring a perfect seal achieved by magic) they be entrances at the ground level and above no matter how great the stone work, natural tiny gaps in the natural rock forming the walls and ceiling...in addition to any design features like windows or porticoes?...mean that air would tend to enter through the door and exit through the gaps.

The direction depends on the exterior temperature and the degree to which the manifold is sealed. With the entrance at ground floor being the biggest channel for air, when it's hotter outside thre will be it will be an updraft and when it's colder a downdraft.

Mess with temperatures in a normal house and you can get rain (https://www.wisn.com/article/wild-temperature-swing-causes-indoor-rain-for-some-homeowners/15066090), but mega factories have been known to have their own weather systems (https://maps.roadtrippers.com/stories/boeing-factory). I don't know if this effect scales up linearly, but your mountain room could have near-permanent cloud cover and/or experience fog during a downdraft.

If the building has doors that open and close, there'd also be big draft...like, massive, each time they were opened. If there was more than one set of doors open at the same time, there'd be a pull from one to the other.

I know building science somewhat, but not much meteorology, but I suspect rapid change in air pressure or localized temperature could create some pretty alarming storm-like conditions or even tornadoes. Caster stuff that creates fire or heat (or lightning) could trigger internal weather badness. The huge draft would also make an conventional fire very likely to go out of control (given any fuel) very fast.

The building and room would also have moisture issues...like, lots of them.

The same rock fissures that allow passage of air allow water infiltration...so if there's a cold season where the mountain cathedral gets and ice cap and a warmer season where some of the melts, there's going to be a riverhead running down the side of the cathedral mountain, and at least some of that water will get inside the building. At which point you pray that the inscrutable builders put in self-maintaining drain system because...water goes from high to low via the path of least resistance.

If that floor is perfectly flat, the whole place floods evenly, but more likely there's enough unevenness that there'd be semi-permanent pools and, quite possible, streams of water trying to find their level by exiting through the front door. And again...if that door spends a lot of time closed...the people opening are going to get a big surprise.

I'm not sure about it, but I suspect that fungi and stuff like lichen would do well in the setting. And that might attract stuff like insects...and at some point it's potentially a cave ecosystem. A lot would depend on how dark it was.

The stone...and its many striated layers of different kinds, if it's a carved mountain...would effects both air and water effects. Lots of think stone exterior is effective more insulation, so temperature difference between outside and inside would be greater and thus draft and "weather" more intense when the door's open. If any of the stone includes water-soluble minerals, there's going to be stalactite and stalagmite formation, and erosion would take a toll of floor, creating deeper pools and channels. Cut stone also has on ominous tendency to off-gas--specifically the carcinogen radon--which builds up inside stone exteriors.