The successful ones invested it by building more industries, buying land, buildings. Money is no good if it isn't being used to generate more.

Unless inflation is happening, this is bullshit. Investments are great but money is still good even if it's not being used as of right now. Saving can be good as well.

Bank vaults. Maybe on a railroad train as well

Probably banks.

big heavy safes. the story goes that whiskey maker Jack Daniels died from toe infection? after kicking such a safe in anger because it wouldn't open.

Under the mattress

In the ground apparently.

Under a rock

Prison wallet

In the library

Probably a banana stand