One of the things I like to do is think about interior spaces in video games.
If you look up "interior spaces in video games", you'll find a lot of guides about level design, but that's not what I'm talking about. I'm talking about places where people work and live.
If you study interior spaces as where people work and live, you'll find a lot of real-world interior decorating/architecture stuff, but it's only mildly applicable to video game spaces. An avatar that appears to live in a space needs to be treated differently than a person who actually lives in a space.
I started thinking about other kinds of interior design, and the answer was obvious: set design.
Of course I'll start with Star Trek, because Star Trek had a whole lot of interiors. The audience had to believe that the crew could live in the ship, 24/7, for months on end. Because of that, the interiors were often surprisingly well-designed.
In TOS, the sets were designed pretty freely, and the result is that the original Enterprise had a claustrophobic feel. While it is believable that people could operate in that environment, it was a bit too cluttered to "feel right", especially for a video game. Recreations of interiors in TOS-style have been done many times in video games, but they are usually scaled up dramatically. This backfires: while they no longer feel cluttered, they also no longer feel coherent.
To talk about a specific example, in TOS the quarters were a lovingly-crafted "L" shape with a signature curved half-wall between the bed and the living space. This room is very practical and makes a huge amount of sense for a crewmember living alone, eating in the cafeteria. In STO Academy, these rooms are recreated, but they are scaled way, way up to hilarious sizes. The whole point of the original room was it was tiny, cozy, utilitarian. The same room scaled up appears bizarrely empty, with a tiny bed surrounded by acres of empty space on either side, then the signature half-wall.
Another problem with the TOS sets is that they aren't third-person-camera ready. While they work pretty well for TV cameras, even then there were times when the directors were clearly struggling to find a good angle.
Along comes TNG, and all these problems went away.
The hallways are gently curved and organic. The gentle curve was a boon, keeping scenes intimate without making the corridor feel chopped up or confined.
The rooms in TNG were huuuuge. This was a ship with families on board, not a military vehicle, so it was quite posh. Even small, functional rooms like the transporter bay were much larger than they needed to be. This was a huge boon to the directors and cameramen, of course, but it's also a huge boon to game designers: upscaled spaces are much easier to navigate and understand when playing a game.
To counteract the naturally "boxy" feel of large rooms, outside walls tended to be curved both vertically and horizontally - a conceit that fits the ship's saucer section design. This completely destroys the squareness of the rooms and gives them a futuristic feel at the same time. In fantasy games, this same sort of thing would be accomplished using wooden structural beams and canted ceilings.
The quarters in TNG were a stark contrast to those in TOS, and were so much better that Kirk would have cried. In general they were split into several rooms by open, full-height gateways. Although it was never made clear, it looked as if the wings of the gateways could be slid shut to create proper rooms. It was a very livable design for crewmembers not living alone and eating inside.
Strangely, nobody's quarters were ever messy.
The signature half-walls made a reappearance as dividers against the curved wall. They worked to break space up without closing space off, making them a boon to the cameramen.
Video games continued to scale these spaces up, leaving vast swaths of empty carpet.
Babylon 5 had most of the same concerns as TNG in terms of living space, but took everything a lot further. They didn't modify the walls or ceilings to diminish the box-like effect of their interior spaces. Instead, none of their spaces were box-like. They bent over backwards to make nearly every interior space a jumble of curved and straight spaces, with plenty of oddball "pocket rooms" that weren't actually separate, but completely broke up the room's footprint.
Back to Star Trek. DS9 took another approach, breaking up the shape of the room by creating little landings above and below the typical floor height. When that didn't fit, they went with an aggressively curvy look and very high ceilings. The good news is that this approach worked well when scaled up for the video games, as the platforms, curved walls, and vaulted ceilings all scaled up at the same rate as the amount of carpet.
Now, if we're going to think about video game interior spaces, we need to take these lessons into account.
Again, not talking about "level design". Talking about virtual spaces virtual people live in.
What will work will probably depend on what sort of camera the game has. A first-person camera will always be able to see the ceiling, for example, but a third-person camera will only rarely see the ceiling. Similarly, a third-person camera means that the camera can get "caught", leaving pieces of the level geometry obscuring your view of your character... and contrariwise, you can slide it around to get a much better view of the area than your character might actually have. This means that islands work well in first person view, while L-shapes are clearer in third-person view.
I don't being these up for game balance purposes, but for design purposes. What the player will see will be what the player notices. A third-person game can employ L-shapes and pocket rooms as part of the general design, but in a first-person game those would be secret corners you would need to scout out manually. On the other hand, the ceiling and the height of the floor are critical parts of the room design in a first-person game, but in a third person game one is invisible and the other is played way down due to the higher camera angle.
The other aspect of this is the NPCs that inhabit the space. Right now, I'm busily building a library to help them feel like they actually live in these spaces by giving them various kinds of clutter, but there's also just the way they use the space while you're around.
This is one thing Skyrim did very well for its time, and came in two pieces.
The first thing was that the NPCs would putter around. Especially in Riverwood (the first village), people would move through their houses in ways that made the houses feel real, such as the way they would cut around the table and interact with a bureau in a nook, or stand at the top of the stairs to watch you as you rummaged around their basement.
The second thing was that the design of the houses gave rise to certain kinds of interactions between the player and the NPCs. This was a delicate thing, and if you didn't play a thief you may not have noticed.
For example, most houses had the upper floor overlook the lower floor, giving NPCs a much wider range of vision. This added a very nice, rustic feel to the houses in addition to adding texture to your attempts to look around or hide. Many places had multiple beds in clear proximity to each other, making it a high-risk situation to navigate around or steal things at night.
These could be punched up considerably if we understand what we're trying to do.
In general, here are some ideas I want to explore as I develop houses for this fantasy prototype:
1) Structural beams, both horizontal and vertical.
2) Complex ceilings - vaulted, canted, curved, etc. Structural beams integrated, of course.
3) No heating ducts, so most areas have open connections.
4) Raised/sunken areas, perhaps integrated with features such as plumbing, natural rock, stowage, tables, etc.
5) Second floors which are openly connected to the first floor, not walled off.
6) "Light" doorways, such as beads, sliding doors, or curtains. Allow NPCs to adjust them properly.
7) Partial walls such as half-walls, integrated counters, folding screens, etc. Allow NPCs to adjust them if possible.
8) Variable room configurations - bedding that gets put away, or has screens erected between beds only at night.
9) Adjustable ventilation such as windows, liftable walls, and propped-open "skylight" ceilings. Below-floor too, perhaps.
10) Large, glassless windows that swing open, lever outward, etc. Drapery across them for cold times. Again, NPC-useable.
11) Pocket rooms that break up the footprint of the house. Integrate them into exterior spaces if possible.
12) Curved regions, most vertical, but some horizontal. Horizontal curves are probably made of rock or brick, not wood.
13) Non-orthogonal walls to break up boxiness.
14) Multiple kinds of walls. Mix bricks/rocks, wood, plaster, etc. This was actually pretty common, and would look neat.
15) Organic shapes, probably mostly due to draped cloth or wooden "ribs".
16) Focus on which spaces belong to which NPCs and how much that is respected.
17) Focus on how the NPC's behavior interacts with and keeps an eye on other NPCs, including through windows. Ideally, make them interact with each other across these spaces instead of standing toe to toe and chatting every time.