THE TOWER is ornate ivory antique masonry: locally rectilinear, globally radial, cathedral-like in spatial openness, enormous through repetition, and transformed by ruin. It is only ever "the Tower".
ALTITUDE changes environmental state rather than architectural civilization.
THE WORLD outside is mundane, many-realmed and far away. The frontier is a crossroads that no realm owns, held together by a treaty, in a valley watered by the Tower's own river.
HUMANITY remains readable medieval fantasy and is allowed to use familiar roles/cultures when that helps gameplay. Nobody has magic.
THE POWERS want the Tower for different things and spend other people's lives to get it. The Cartographers hold the only way back, and they rule the neutral city-state the realms tolerate because it keeps the stone flowing.
SOCIETY ranks by height, speaks a trade tongue, and splits four ways over what the Tower is.
PORTERS turn logistics into silhouette and mechanics, and carry the one thing the Tower will not give: food.
CREATURES are biological and alien, mostly inedible, and standard enemies remain cheap enough to reuse in a side-on autobattler.
MATERIALS express three relationships: humans manufacture; creatures are processed; Tower fragments are preserved and adapted around.
TOWER TECHNOLOGY should always remind the player that humanity is exploiting tiny broken pieces of something incomprehensibly larger.