One thing I didn't expect was the sheer size of it...

One thing I didn't expect was the sheer size of it when you look at it from inside. And this was built 1500 yrs ago. Of course it must have been the 8th wonder of the world with its mosaics of gold had it not been ruined by Ottomans by plastering over masterpieces and painting. Nevertheless, this should be the first thing you visit in Constantinople/Istanbul.