Ayasofya

This place is so extraordinary that it deserves its own post.  In 532, the infamous Nika Revolt (which was fomented by chariot-racing factions for a variety of very weird reasons) destroyed the old church (known as the "Large Church") and much of the city center.  Dismayed by the populace's attitude, Byzantine Emperor Justinian called the rioters to assemble at the adjacent Hippodrome to plead purportedly for calm.  Once gathered, troops under the command of the great Balisarius sealed the exits and fell upon the crowd with swords drawn.  Between 30-50,000 people were killed.  Nobody really knows how many.  This instantly restored calm.  But Justinian felt pretty guilty about the whole matter in the ensuing days and came to believe that building the world's largest church was a way for him to make right with his Jesus.  It took 10,000 workmen just five years to complete it.  In contrast, both the cathedrals in Rennes and Cologne each took more than 600 years to complete and the cathedral in Strasbourg, which was begun in the 13th century is still not complete. Anyhow, Justinian dedicated it to holy wisdom or Hagia Sophia, which is an abstract idea and not a person.  Not only was it the world's largest church, it remained the world's largest building for centuries.  Mehmet the Conqueror made it into a mosque, like, the day after the Turks took over the city in 1453.  Today, it's a 1,500 year-old museum.  Have a look:

 

OK, so ending with a shot of the inlaid marble is pretty unspectacular, but just imagine these reaching up 50 feet and wrapping themselves all round this massive building.  That's pretty impressive, no?  I stayed here for two hours.  I could have stayed all day, but the tour groups - Oy! - they eventually filled up the entire place.  As you can see, the church is not in completely pristine condition.  Well, I doubt any of us would look this good as we approached our 1,500th birthday.  From what I've read, its construction wouldn't have been possible without considerable architectural innovation, as well as some pretty intense mathematical calculations.  It may not seem like it today, but domes were really tough to build back in the day.  Thanks to the talents of architects Isidore and Anthemius, the building went up with only a few major crises along the way.  And today, it still stands, ready for mass or Friday prayers or whatever religion you want to throw at it, but functioning best as a museum and a testament to human devotion and achievement.  And guilt.  Don't forget that.