To build a folly is essentially to do something a second time, something at an inopportune moment. That something is always the memory of something forgotten, about which we can paradoxically say "There it is again."
Follies were misunderstood, purposeless constructions. They were often only small, extravagant gestures in a garden, easily whisking off the imagination to distant lands, a sort of time capsule built to awaken the memory and induce surprise in passers-by. They marked locations, organized secondary paths in a park, or simply predicted the arrival of better times—a demarcation, a sacred spot, a mysterious trail, a hill whose tragic rocky nature begged for a tower, a party, or the arrival of summer.
“It is demonstrably true that things cannot be other than as they are. For, everything having been made for a purpose, everything is necessarily for the best purpose.” — Professor Pangloss
The inglenook, the gazebo, and the porch swing also have strong definitions of their spaces. They are each a bit like a little house set off for a special thermal purpose. They might be termed "thermal aediculae". Although the term aedicula is most often used in conjunction with a sacred or ceremonial little house, it can also be used to describe any diminutive structure used to mark a place as special.
Summerson contends that there is a basic human "fascination of the minitature shelter." Perhaps this is because the aedicula intensifies ones experience of the place by working someone like a caricature. By reducing some things in scale, it exaggerates the importance of other things, most especially the size of a person in relation to the space.