Limbo is another name that Catholic teaching gives to purgatory.
In Catholic theology, purgatory is where some souls go before they are allowed to enter heaven--the souls there do not deserve hell/inferno, but they don't exactly deserve heaven/paradiso yet either, hence they are in limbo.
Some other dictionary definitions:
...the souls of unbaptized infants are in limbo
a place or state of restraint or confinement
a place or state of neglect or oblivion
an intermediate or transitional place or state; a middle ground
In Terragni's Danteum, purgatory is designed as a "room" that is both (equally?) inside and outside--the transitional place. Supposedly, this is to have an uneasy effect, being neither inside or outside, but I think you can look at it positively as well, being both inside and outside--the center of the Villa Savoye is a perfect (positive) example.
Using this analogy re: the architectural promenade, when one is at this point in the path, then (I assume) one can experience/learn from/take advantage of both (heaven/hell inside/outside) realms.
fact check and some proof
I'd say the real shell architectures were those caves some humans used to live in, and beyond that architecture became an applied shell, and going to an(other) extreme, a space station is all shell, but hardly natural.
fact check and some proof
I see your point about architectures that fulfill nomadic intentions, but I also see mobile homes, trailer parks and even just automobiles as architectures that fulfill nomadic intentions better than hotels. Hotels fit more the oasis typology/metaphor, acting as both waystation and/or destination.
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