The Elements of Social Architecture:

Published in 1977, Christopher Alexander’s A Pattern Language: Towns, Buildings, Construction contains the collective wisdom of world cultures on centuries of building human housing. It had a resounding effect not only on architecture and urban planning, but also on software design. In it, Alexander and his co-authors explored 253 architectural design patterns. For example:

203. CHILD CAVES
Conflict: Children love to be in tiny, cave-like places.

Resolution: Wherever children play, around the house, in the neighborhood, in schools, make small ‘caves’ for them. Tuck these caves away in natural leftover spaces, under stairs, un”

(Via A List Apart.)