You can put it it a bank CD and be guaranteed to get your money back plus some interest, but there is no guarantee that the money will buy as much in the future as it does now.

You can buy an inflation-indexed bond, but if you redeem it before maturity there is no guarantee you will get all your principal.

The best investment is a diversified portfolio. You can find many diversified "asset manager" mutual funds. If you possibly can, I would encourage you to look at buying one of those inside an annuity. That will make it nearly impossible for you to touch it until you are 59 1/2, which is a good thing. It also takes away all the capital gains and dividend tax headaches. Just be careful of the fees. You want a no-load annuity wrapper on your diversified mutual fund.