[javert]

Instead of having a vault with just 100M euros, it probably makes more sense economically to build a huge vault that can store billions of euros, and then charge people to use the vault.

[tempestn]

And call it a bank. And as long as you're charging less than it would cost them to store money themselves at scale, that would work...

[javert]

It's not really a bank because you aren't making loans because interest rates are negative.

If interest rates were positive, you would want to make loans, but then nobody would want to put physical euros into your vault in the first place.