I've found Pony is way more picky at backgrounds than SD1.5 was (you could throw really random locations at it and they'd blend together into something interesting), and even some stuff it recognizes doesn’t always get generated well. Here I’m listing tags I’ve discovered make good (or at least not blatantly non-Euclidean) backgrounds on their own (without additional LoRA). This is mainly to keep track of it for my own purposes (read: I edit this without change-log when I find something neat. I try to keep new stuff at bottom), but sharing this means other people can share their discoveries in the comments. (Backgrounds are an option for one of those big prompt comparison chart articles for anyone with the will and resources to try .)
Tags after a comma mean they’re supporting tags that make it more fleshed out and I haven’t really tried using them without the first listed. A ? means I've had a good result with it but haven’t experimented with it (or the string in parenthesis) enough to say for sure it’s useful or if it’s just other prompts/the LoRAs that in the mix doing the lifting/getting lucky.
Outdoors:
(badlands, crater, cliff, mountain?)
beach, sand, ocean,
canyon
castle background
city, cityscape, street, on roof,
desert, sand (, mojave desert?)
fantasy village background
farm
field
forest, trees
laboratory?
mountain
onsen, steam, wet, water
park
(ruined city, toppled skyscraper, rubble?)
slums, building, outdoors, garbage, rubble, ruins
wasteland, grey ground, rock, bare tree
plains, grass
alleyway, brick wall, trash can, dumpster, graffiti,
Indoors:
bunker interior, underground bunker,
castle background, throne,
catwalk (\modeling\), stage lighting, crowd
classroom, desk, blackboard
colosseum background
fantasy village background
(fantasy ruins background, maze, labyrinth?)
hallway
living room, couch
shower (\location\)
spacecraft interior*, (spacecraft bridge?)
arcade, arcade machines,
store (adding adjective for store type?)
casino
club (needs "strip club, pole" in negatives)
bar, bar (place), saloon background, (the first two combine to make the bar's bar appear)
shouji, fusuma, tatami (Do not use "Japanese architecture". May need negatives like doorknob, outdoors, open door, window)
middle eastern architecture, palace, cushion,
Supporting objects:
building
carpet
ceiling light (great if you want ceiling to appear due to depth or angle)
grass
overgrowth, vines,
scenery, landscape
sidewalk
tree
trees
waterfall
path
wall/floor (ceiling works, though I've found ceiling light to make more natural in settings where it fits)
river
mountain (I've yet to figure out anything for making a character in the mountains though)
Genres with an influence on background (beware their influence on other parts of image)
science fiction
cowboy western
fantasy
Known to PDXL but poor results:
“Athletics Field” and/or “Track and Field”
Basketball Court
Bedroom (This is one of the worst offenders. Especially if doors or windows are present. Some checkpoints tolerate it better than others, but it’s rarely great. I've found it is pretty good at checking for overbaking in epoch pics though.)
Japanese architecture (this one needs heavy supporting word use to make clear which era/kind of Japanese architecture you mean, and I've concluded that you're better off just calling the elements you want)
*This one will alter the overall theme of the background a good deal.
(The cover image is "score_8, score_8_up, score_7_up, source_anime, anime screenshot, no humans, scenery, landscape, canyon, waterfall, outdoors" in WAI-ANI-NSFW-PONYXL