Start a business or buy a business so that you can make that $750K into millions. The barrier to entry in many businesses is startup-capital. So I would look for businesses that have that barrier and start one OR you can buy a business and expand it. Many examples include: you can buy a hotel, restaurant, real estate, and many more. A good place to look for businesses is craigslist (believe it or not).
It all depends what kind of entrepreneurial spirit you have. I know that if I had $200k right now, in a year or two, I could make that into millions (this will involved lots of hard work). If you are not willing to do work then you can buy "absentee business" where the owner does not have to be there.
You can also become an "Angel investor" in a startup. But there are many startups and very very few make it big, so big risk if you do not know what you are getting into.
Just my thoughts, it all depends how hungry you are and how hard you are willing to work.