Would you like to explain, for slow-witted people like me, ;-) why you have a rather negative attitude towards this project? (Underground rooms can possibly also serve as shelters.)I have two small counter questions: 1) how old are you? 2) what do you smoke?
I hadn't read it that way before. Then it will be especially expensive. An underground garage is a commercial use (at least at the size you have in mind), which could already be prohibited as such. In addition, there are high requirements for fire protection. The access/exit will also be challenging.The lower part is intended for an underground garage (also accessible for the adjacent rental buildings). The part above as a large workshop/ storage and laboratory. Also, I somehow like such buildings.
Discussing the advantages and disadvantages of a basement? Then it requires a discussion based on the actual planning. Because the fact that a basement is usually dark and underground should be known ;-)Could we not discuss the advantages and disadvantages fully?
Maybe one of the James Bond supervillains can recommend their planners – they even manage to convert entire volcanic islands into world-destruction factories without anyone noticing. ;)
Move to the Ruhr area. You will very quickly hear stories in which (former) miners have subsequently expanded their row/colony house downward by hand.
Whether urban legend or truth, I cannot say.