It took me a while but I tracked down all the Truth glyphs and was able to decode them and
barely sometimes had to look things up on the Internet. (I hadn't been to Florence for a while and found it very difficult to match Italian names to actual locations.) And some of those photo hunts were practically impossible. Still, I was able to use my own brain to solve some of them, including that final passcode.
The stories you come across while unlocking all these: Holy crap.
The "missing link" you read through in the final decoding session: Holy crap!
The video you get after decoding everything: (Neo) Whoa. (/Neo)