Back in the early to mid 20th century, doctors prescribed lots of fresh air year round; my mom hated pushing a baby carriage so would drive her convertible around Fort Wayne in the middle of winter with the top down and my sister in the back seat. Carrie McLaren at BoingBoing shows an alternative, a little clip-on window crib. She notes that "According to The Health-Care of the Baby by Louis Fisher (1920), window cribs were "admirably adapted for city apartments."
It is also an interesting solution to the problem of getting a bit more room in a small apartment, sort of a high-rise version of a garden shed.
Modern Mechanix shows an English version from 1939, noting:
Enclosed in a wire cage suspended from an apartment window, English children play in the sunlight and fresh air while their mothers are busy with housework. The cage, made of wire netting is strongly braced and is guarded on the apartment side by a cloth net which prevents children from crawling back into the room. Loaned by an infant welfare center to families with no gardens, the portable balcony is apparently popular with children and mothers.
Another option is Hammokum , although I am not certain I would want to put children in it.
Then there is the Rucksack House in München, Germany from 2004, designed by Stefan Eberstadt.
The Rucksack house offers a way of improving housing quality on an individual basis.It is a direct visual sign and reactivates the idea of the self-built anarchistic tree house, but one that is more prominently placed and structurally engineered. New space gets slung onto an existing space by a simple,clear, and understandable method.
So many clever ways to get a little more space!