Anyway, thanks internet, for taking away 2-3 hours of my life to look at multi-million dollar mansions for sale in my area as well as have a merry old time contemplating what I would buy / do if I were suddenly granted $100 million.
(Favorite idea I have not seen anyone on the Reddit thread mention: buy, restore and sell older houses, not so much for profit as for love of the architecture and hatred of change. Historic mansions in danger would obviously be the biggest lure, but there are also plenty of perfectly nice little 60-100 year old family homes on the real estate site being advertised as 'needing TLC' that will probably end up torn down by developers, and I would greatly enjoy being able to provide the capital to shore them up and give them a new lease on life.)
P.S. Other considerations now include "this immersive shower tomb that is officially known as the Experience Shower . . . colloquially termed the rave shower," as detailed in this perfectly delightful Jezebel post:
"I would forgo all the designer clothing, all the expensive jewelry, all the cabs-everywhere-lifestyle that I assume wealthy people enjoy to fulfill just this one wish: to be able to clean myself every morning in a shower equipped with a waterfall, body jets, flashing LED lights, aromatherapy, sound effects, music of my choosing and, if I were extremely rich, a foot massager."