Unlike old overcrowded cities, Las Vegas tends to fully erase all traces of old buildings and streets. We don't have abandoned subway stations, or othe such modern relics. For the moment however, Las Vegas does have a mystery button.
At the intersection of Las Vegas Boulevard (The Strip) and Spring Mountain Road there remains several buttons for pedestrians to press in order to effect the crosswalk traffic lights. This despite the crosswalk having been removed some time ago, when the elevator and escalator crossovers were opened.
This is a rather busy intersection, and was always dangerous for pedestrians to cross. The four corners contain The Fashion Show Mall, Treasure Island, Palazzo (under construction), and Wynn. Fences are up to ensure pedestrians remain on the sidewalk, and use the crossover to cross the intersection.
Nonetheless, the street crossing buttons remain from when this intersection was crossed on ground level.