Gringotts Wizarding Bank

Enter, stranger, but take heed
Of what awaits the sin of greed,
For those who take, but do not earn,
Must pay most dearly in their turn.
So if you seek beneath our floors
A treasure that was never yours,
Thief, you have been warned, beware
Of finding more than treasure there.

The centuries-old bank is run by goblins, and they alone know the secrets of the twisting underground passages and the enchantments (and creatures!) in place to defend against intruders. The goblins have a code that forbids them to speak of the bank's secrets, and would consider it "base treachery" to break any part of that code.