I leave it to you to add the details. Bomb-shelter technology (filters, running water pumps and air venting by bicycle peddling, etc.) can be used in this structure. It can be built over a long time without significant degradation of materials for less money and labor than what would be required by many of the other designs discussed. This design is wonderful as a meditation room or little kiva and such usage would do best to set the stage, vibes-wise, for a hide-out in troubled times!