Here is something that mystified me about Manhattan I have only recently puzzled out:
These big padlocks that decorate the fences and tree wells on the streets with brownstones. They are key safes: these allow housekeepers, air bnb, repairmen and estate agents access by a combination— there are more and more of them every year.
I feel like there ought to be a better solution— still this beats using some door lock app.
