Gringotts Bank

Gringotts bank is guarded by goblins in fact there are two out in front of the main gates and there are stories of great dragons that guard what it holds.

To create a account here in gringotts, you must put in 10 golden galleons towards your account
Then every 4 weeks you get 5 percent inerest added on to what you have in your account

No real money needed for this