Fun fact: One of the most closely guarded pieces of paper in those offices are the tax receipt forms. Because if you can produce a tax receipt it's good as cash for meeting your tax obligations.
"Hi, IRS? I've got a billion dollars worth of 'other, unspecified' income I need to pay taxes on in Cash. My name? Uh...."
If the person on the phone had said “Capone, Al” instead of “Uh…” he’d possibly not gone to jail.
Even ill gotten gains are taxable and the theory of one crime at a time suggests that even “other, unspecified” could be with paying taxes on to reduce the likelyhood of successful criminal persecution.
They have a nice page about how to make an appointment (recommended 30-60 days in advance): https://www.irs.gov/payments/what-to-expect-when-you-pay-cas...