APART FROM the occasional wailing siren, New York City is eerily quiet—so quiet that you may be woken by birdsong, says Beatriz Colomina, an architectural historian. The city looks different, too. Pedestrians have taken to the roads, which are almost empty of moving cars. Those widely spaced walkers can look up and see things that they missed before. For Ms Colomina, it is an ideal time to appreciate buildings.

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