The housing crisis explains this whole picture to me: Landlord has bought up these old houses (on back-to-back lots, sharing a backyard) and renovated every floor including the attic into living spaces. By law, an "apartment" needs to have it's own exit for emergency needs, and for the security of being able to lock a door from access by other tenants (who are essentially strangers). Thus this admittedly creative complex of stairs in order to maximize the amount of rent the owner can squeeze out of this property. Renting an attic space? No no, it's now a "private suite" with it's own entrance.
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