Absolute Safest Investment for Inheritance

As a former financial advisor, my advise is to find a one-time fee only financial advisor.

If anyone were to answer this question without you asking a bunch of questions first is doing you a great disservice.

Here are some factors:

1- how old are you? 2- what are your current debt situation? 3- what are your current investments? 4- what is your current income? 5- what is your current liabilities? 6- when do you plan to use this money? 7- is the 800k in some sort of inherited retirement plan like a ira or roth ira? 8- what is your current marginal tax bracket?

Etc, etc...

You'd be surprised how big of a mistake you can make here by doing the wrong thing.

One thing you should get out of your head is that there is zero risk. Even keeping it all in cash in a checking account has risk.

CD ladder isn't a bad choice. A treasury bill ladder could also work and might actually fit as well. The risk is in a rising interest rate environment the t-bills you buy now will be worth less in the future. You'll still get the dollars in absolute terms but it might buy less. Too bad you can't buy I-bonds past 10k a year.

Also the biggest risk in your plan is the "leave alone and not manage". There is manage a little, manage a lot, or pay someone to manage it for me. Leaving it alone and not managing it has its own risks.

How quickly do you need to be able to access this money in the future? If immediately, put it in high yield savings accounts. If you can tolerate a bit of a delay then a CD ladder or a ladder of treasuries is the way to go. If you're using banks for either savings accounts or CDs mind the FDIC limits. You'll probably need to split that much across multiple banks.

Based on you looking to have 30k per year, maybe consider looking into the Financial Independence community and their considerations on this. Sounds like you could be pretty damn close to FI with a conservative safe withdrawal rate.

3 month T bills may be appealing at current interest rates.