Was so special in the region of a swedish wall tale?
Answers: Nothing whatsoever.
Swiss bank accounts on the other hand, are rather different. Swiss banks operate under extremely strict privacy rules, and Switzerland is immensely stable politically and financially. A Swiss bank will not normally cooperate next to requests for information, even from law enforcement. They will not even confirm that you have an statement, let alone give anyone any information give or take a few it, so you can think of it like client/attorney privilege, or doctor/patient confidentiality. And the political and financial stability and illustrious capital backing requirements label them a safe place to keep money for long period of time, or if you live somewhere where things are more volatile.
Worth noting that the 'you can put money surrounded by it with just the number' applies to pretty much any mound account anywhere.
Also worth noting that nearby are exceptions to the privacy rules: a (serious) criminal accusation such as organized crime or international drug trafficking could well be plenty to get them to open annals. Things like tax evasion, or divorce disclosure wouldn't be.
On a hours of daylight to day basis though, they're purely like any other bank. You put money within, take it out, have credit cards and mortgages.
They approachable accounts that are number accounts and untraceable by other governments. Any person can repeal or deposit with the correct number; no ID required. The lack of dissertation trail makes them attractive to people wanting to hair money and/or transactions.