Ancient history: Roman seawater concrete. The magic of self-repair. Temple mechanisms and the modern disbelief in ancient excellence.
(They really DID move monoliths, build automata, and enjoy the hell out of life. Every time Herodotus gets proven right about something else, I laaauugh.)

Polychrome: Supervillain lairs, possibly Fortressa's, with heavy technological defenses. Anti-teleport mechanisms.

Any: Pocket dimensions mediated by machinery, aka where all my left socks go.