Dominating the skyline of Mainz and commanding center stag of the Altstadt, is the Mainzer Dom, also known as the Cathedral of St. Martin. The Dom is over 1,000 years old and the episcopal see of the Bishop of Mainz. Much of the cathedral, except for the vault, was destroyed during WWII, but, as you can see, it has been fully restored and now serves as the striking backdrop to the city’s major festivals and the thrice-weekly market.
Today, the Dom is open to the public and holds regular services and concerts as detailed on its webpage: http://www.mainz-dom.de/index.htm
More on Mainz can be found here: http://leaping14.wordpress.com/2014/04/16/herzlich-willkommen-a-tour-of-mainz/