On the outskirts of Krakow, the Wieliczka Salt Mine is an amazing Unesco-listed underground world of wonders. The mine has been worked for 900 years, and used to be one of the largest salt mines in the world. It is comprised of over 200km of underground passages and 2000 caverns of various sizes. Today visitors can take a guided tour of the mine, starting 64m below the surface and ending 135m below the surface. Highlights include a chapel carved entirely of salt, where Pope John Paul II once gave a service. Tours are conducted all year round in various languages.