I am always fascinated to read and watch programs on extreme and lavish construction projects.

Recently I watched a thought provoking documentary on the raise (no pun) of underground extensions in suburbs of London. Of course, these weren't your common-or-garden London properties selling at a "mere" million pounds, but multi-million pound projects in areas such as W8 and SW3.  

The documentary, as the below article touches on, highlighted some huge advantages to investing in underground projects, not least expense, decreases in thermal / acoustic levels, and space.  One huge disadvantage, which I doubt the mega rich give a tinkers cuss for, is neighborhood disruption; noise of project work and potential damaging affects on neighboring properties in the form of subsidence.