Eruvin 84: The Sages as World Travelers

When the Gemara not only interprets, but reinterprets the Mishnah. Specifically, the two-story homes, and those who live in the upstairs homes. "To the courtyard" - both residents really do have access! The mishnah is contradictory, to what we know from everywhere else - so the Gemara's reinterpretation seems necessary. Also, the case of two-story homes, where the top story balcony hangs out over water. Namely, another "reality" for eruvin. Yet another very real architectural set-up for Hazal.