^ This.
Once I got to about 5 years left on my mortgage (about a year ago) I really started socking it to it with extra principal. I have since knocked off about 2 years, and have about 2 years (instead of 4) left. I felt that there was no way to guarantee a 5.5% return (my mortgage interest rate) over a 5 year period. And I wanted the security of paying it off.
I would pay off my debts, buy a car and house. Both will be modest.
I can’t help suspecting that a lot of the ‘instant millionaires blow it all’ phenomenon is because what we see is mainly a sample of people who think playing the lottery is a good idea.
Yes people in the thread may plan to ‘waste’ money on peace of mind, paying off debts when they could make more money by not doing so, but that is something that at the least leaves people more financially secure than before they got the money. It’s not ‘buying a yacht’ foolish.
For myself, I’m currently below poverty level; it would be life changing. I’d get a house (small, with a large garden), or, if I could find one at a decent price, a smallholding. I’d go to university, so I could try and get into a career I found interesting, and invest the rest for emergencies or retirement. I don’t think in $, so I can’t really put an accurate price on things, but I think that should be doable.
I would like to be comfortable, but not the richest corpse in the graveyard- my grandpa tried that one, and I saw the joy he didn’t get from it.
I’d post what I wanted to do on an message board, so I could be judged and looked down upon.
But only after the check clears. 
Buy the house I’m renting: ~50k.
Improvements to the interior and exterior of the house I’d like to make: ~25k
Buy a Tesla Roadster: ~100k.
Buy Mrs. Homie a Jeep Cherokee: ~30k.
OUTRAGEOUS, top-of-the-line, no-expense-spared vacation to Disneyworld and central Florida: ~15k.
Various tech things I want (new gaming system, TV, computer, etc.): ~5k.
The rest would sit in a bank and earn interest until the day I died.
Good plan; I bet it will work. 
$10,000 off the top to hold a ‘spite’ party. I’d invite everyone who’s ever treated me badly, build them up to a sense of false hope that I just might be sharing some of this windfall, let them suck up to me a little (oh heck, a LOT), then at the end of the evening, thank them all for coming and announce that hell would freeze over before I’d give them a dime of it. Petty, yes, but so much fun.
Next, I’d spend whatever it took to charter a sailboat and crew and spend a year sailing around the world. No rush, no worries, stopping and sampling interesting ports of call and let the sea erase all the years of corporate stress and strain.
Upon my return, I’d buy a small house (it’s just me, after all) in the mountains and a condo in the city where I work. Finally, I’d buy a top quality brand new car with all of the amenities you could ever want.
Whatever remains would be invested carefully for my eventual retirement.
And if I didn’t need all of it, whatever remained would be put in a trust upon my death for my grandchildren’s college education.
Not the most exciting agenda, but all of the above would make me deliciously happy.
Paying off a mortgage can be seen as investing at the mortgage interest rate (less tax break) but it can also be looked at increasing equity in a house. Which is fine, but the crash shows us that home prices are not safe either. You might be safe from a default but you can also lock in a big loss if you have to move.
Houses in my neighborhood have swung multiple $100s of thousands of bucks between the height of the boom and the depths of the crash and today.
My plans would be really mundane. I’d spend most of the money on things I’m already planning on: a house, a car, and some dental work.
Uh, unless you plan on defaulting and declaring bankruptcy (which should not even be a contingency plan if you get a million dollars), you’re going to have to eventually pay what you owe on the house, not matter what the house’s value is. As long as you’re not planning to default, paying off a mortgage early is exactly the same as paying off any other debt early (well, they are treated slightly differently for taxes), which is equivalent to investing the money with the interest rate a guaranteed rate of return.
That depends on your age.
At my age and my husband’s? Totally life changing.
I don’t need anything. I would know that I could get a decent nursing home or home care, and I would be able to help my daughter. Some would go to church and pet-friendly charities.
Dental work alone might do it in…
(I just had a dental visit and an estimate that’ll leave me $2K poorer. For ONE broken tooth!)
That’s pretty much where we are, but a little farther out. This would accelerate our retirement - or at least the phase in our careers where we have some consulting income, but don’t bother to work full time.
Or do as we do. Experienced money managers (ime) tend to have a 100K minimum. We picked a good one and gave him the minimum, keeping the majority for our own control. We watch what he does with the 100K, and copy that with the rest.
As to the OP: We already have our retirement streams set up, most debt paid down, the kids’ inheritances arranged, and can’t think of much else we want to buy. So a windfall would be invested, with the intent of ensuring our grandkids (if there are any) would have a good source of college/house/life-launch funds.
Interesting assumptions, but way off the mark in my case. I have been in finance all my life, I know the numbers. Paying it off today gives me an instant and (as you say) guaranteed return equal to my mortgagae APR. Investing in stocks over an average 15 year period will likely return 8% per year overall. When you talk about any specific 15 year period it may be more, the same, or less. Ask people who were going to retire in 2009 on their 401k money.
ETA - without far more specific information about the total financial situation, you cannot possibly tell someone whether it is financially prudent to pay off debt (any debt) versus investing the same money.
Pay off mortgage, school loans. With the rest, go to Russia, get me a hot wife, come back here and resume life.
Pay off the mortgage and all outstanding debt. Invest the rest. Do some travelling.
Doesn’t it highly depend on the APR that you’re getting and the time remaining? I mean, if your mortgage APR is like 8%, it would behoove you to pay it off ASAP. But if you’re only paying 4%, the market can underperform by 4% before you start to pull even with paying it off vs. investing. Similarly, if you only have 4 years to go, it makes sense to pay it off- you’re not likely to make much money in such a short period, but if you have say… 15, you can.
This is what I would do. Except that I would definitely buy a home.
As for me, I’d likely just put some in a cash-type account, and invest the rest in a diversified fashion as retirement/rainy day money. We have no real need to buy new cars or pay our house off ASAP.
I would spend some to get our backyard redone- maybe 10k or less. New fences, new deck, better landscaping, etc…