I'd say if you trust yourself:
- Cold Wallet
- Paper Wallet
If you don't trust yourself:
- Bank Vault
- Get a trusted person to hold and keep your Bitcoins safe.
don't do it
better trust your self and save your money at paperwallet or trezor
anyway im never hear about Bank vault accept to saving bitcoin ?
One would create a paper wallet or something and put it in the bank vault, like a safe deposit box.
900 bitcoins must be very big money. It's only possible to earn this much via providing any services related to bitcoin. I believe they must have earned that much money from selling Hardware wallet itself.