We had a layover in Vienna on our way to Krakow so we jumped on the subway and went into town. We hadn't done much research so we just went to the center of the city and walked around. We came out near St. Stephen's Cathedral. The last section of it was finished in 1511. The south tower is 445 feet tall, 343 steps (trust me). 343 is 7 x 7 x 7. The north tower is only half as tall, at 223 feet. A word to the wise, the observation deck is on the north tower!
Here's the wikipedia article and my pictures begin here. Vienna's web site is here.