Various locations. I have been visiting a lot of archeological sites. I think of them as "found" museums, because they're discovered, not created. Excavated, preserved, protected, and interpreted. The valuables may be moved to a specially constructed museum, but the site remains, where it is, whatever it is. As visitors we're supposed to focus on the archeological part, but sometimes I find myself focusing on the supporting architecture instead. Most of it is permanent, carefully designed to protect the site, and support the visitor's experience moving through it.
Buttresses are interesting in a different way, because they appear randomly as needed, to prop things up. The design is often more urgent and less fussy. They can be subtle or prominent in relation to the site.
Many structures are (accidentally) playful with the site.
Scaffolding is interesting for the same reasons. Some scaffolding is famous. At the Parthenon, where it is a constant element, it's become part of our iconic perception of the place.
Rudimentary archeological sites, with no architecture at all (or interpretation), are alive, enjoyed like marginal parks for the view, drinking, etc. Tagging appears, and footpaths develop organically.