All excellent points! I remember reading stories of collapses of whole multistory tenements in Rome being common (which isn't to say people didn't get mad about it). It make me suspect we are too immersed in modern thinking in regards to planning. People got by (albeit with shorter lives and poorer living conditions) with little or no real planning at all for most of history so I can see your point there. Biologically speaking you have two forms of autotroph photo and chemo (sun users or chemical users like the ones you get at thermal vents) everything else lives off of these ultimately. Of the two chemo is comparatively rare, but a big underground vent system with animals and fungus that feed off of the vent feeders would at least be very interesting and fun. Thanks for all the insights.