What you'd build if you had 100 millions?

I'd be uncomfortable with 100 million I did not earn. I'd like to think I would say, no thanks. Instead, I would probably come up with some justification for why I am suitable to control this very large investment.

(You could argue that, given luck, a lot of people receive $100 million without really "earning" it. That may be the case, but that would probably make me uncomfortable also. However, as in the previous case, I'd still delude myself into thinking I earned it by foresight, brilliant investment, or mettle.)

Personal crash safety suit for motorcyclists/extreme sports which could absolutely protect against all damage. I have ideas, which could be applied to other applications, anyone have the $100,000,000?

I'd build a biotech-biogerontology institute for the SENS Foundation and Aubrey de Grey.

I'd try and find a mothballed oil platform, buy it for cheap and renovate it into a luxury hotel with luxury apartments and market it to celebrities as a way to completely avoid the paparazzi and to a wealthy client list. Bars, nightclubs, restaurants and casino's would be there from the start to help clear out people's pockets. It would be self-sustaining with gardens and hydroponics, wind power and eventually wave power, both of which could be sold back to shore to decrease maintenance costs.

If it failed, so what, it would advance the idea of seasteading. If it succeeded I'd attempt to expand the platform, or build another platform within about 3km, so that the platforms could be connected with existing gondela technology.

The idea of seasteading has always fascinated me, but to make it carbon-neutral or even better carbon-negative (encouraging coral growth around the bases, out putting power to onshore communities, etc.) would send an environmental message that the people who care about the environment aren't just a bunch of witless nags at greenpeace but are people who actually want to change the whole world into something better. This environmental message could be capitalized on during expansion phases and used to attract businesses.

In theory you would become a monopolic supplier of all goods. Food, power, housing, transport, would all be owned by your company meaning you can attain income from all aspects of the business and keep it profitable. By keeping the market open, it makes you look friendly and open (consider you own the transportation, so anyone competing with you and winning is still paying you money).

In 40 years time I would be a James Bond-esque supervillain and precisely where I want to be before retirement.