Need help scouting the perfect Horcruxes/ Geocache location

I am working on finding spots inside the loop that represent the horcrux locations in Harry Potter.

The plan is to map them out and Geocache them with my family. I have 6 places decided upon but need a spot that represents Gringotts Bank, the second most secure place in the wizarding world.

Where, inside the loop, would you suggest represents a very secure place/old and well fortified bank? Ideally it is a public place but I'm taking all suggestions.