Not a business center, but if you ever get the chance to go to the The Wieliczka Salt Mine just outside of Krakow, Poland don't miss it — absolutely stunning (and easily accessible by local public transit).

Supposedly, it was one of the Tolkien's inspirations for the mines in the Lord of the Rings. And because it's a salt mine, the air is very clean. They used to send asthma sufferers into the mines as a form of therapy.