A manhole cover in Hiroshima has its local taste. Yokohama has one of Tourist Attractions, Yokohama Bay Bridge.
あ、マンホールが丸いのは、四角だと対角線で置いたときにストンと落ちてしまうかららしいですね。
The reason why a manhole cover is round is because if it's square, when it's put diagonally, it'd fall down.