1,000,000 is enough money to retire on. Talk to someone who knows something about investing and have him set you up with a solid portfolio. You should be able to withdraw 40k-70k a year. With that type of money you can coast, travel, pursue any interest or hobby. Congratulations you have freedom. Don't fuck it up by dumping it all in bitcoin.
Slow down and think.
He's supposed to pay it back, not retire on it.
If I had a million dollars of play money, not something earmarked for retirement, then I would build rental units in Anchorage or North Dakota where the fracking is going on. Rental units in ANC go for $1/sq ft per month. Spend that million dollars on 2 duplex homes for a total of 10000 sq ft (2500 sq ft/home), that's $10k/month income. After overhead (taxes, maintenance, insurance etc), you can certainly count on $9k. Mortgage it, use the rent to pay off the mortgage (leaving you with pure profit), and pay your dad back. Basically, you're just using his money as no interest a construction loan.