The half-buried bunker, disguised as a dune. And to complete the deception, the bunker also moves around a bit... heading now northeast at about 3 inches per day. Though this is opposite to the dominant wind direction, and it won't be long before someone in the far towns notices that this thing is sneaking out the desert, towards downtown. In fact, there seems to be a whole bunch of them (looking ahead to that time, I can see how the bunker parthenogenically reproduced, splitting along its seams to make many many identical copies... which someday, when the group makes it to the city edge, will be stapled to the local concrete, and then offered out as homes to anyone who needs one).