Although I draw the line at an air conditioned anything in the garden - that's almost as weird in a garden as artificially moved water - I'm definitely enamored of the tradition of pit houses. The book Diane alluded to may have been Winter Flowers in Greenhouse and Sun-heated Pit by Kathryn S. Taylor and Edith W. Gregg. The first edition has a 1941 copyright; I have the revised edition published in 1969. I recommend it highly: take it out on a sunny, late January day when you can almost but not quite taste the coming spring, and you'll wonder where these wonderful ideas have been all your life. Jim McKenney Montgomery County, Maryland, USA, USDA zone 7, where the sun-heated pit is definitely a good one to fall into.