We walk over the bridge and into the Scoule Grandi building. Entering in the code provided by Langdon (to ensure you do not visit this location until after completing the rest of the quest), we walk inside and are greeted with a vast array of Renaissance-era art.
How could this be? The artists aren't influencing the government secretly, they're just painting as expected. Where was the secret society we were looking for?
It is here where the "secret" is revealed. We mentioned earlier that the "Republic" of Venice was not very democratic by modern standards. We even visited both the church (representing the clergy) and doge's palace (representing the nobility) to emphasize this, before breaking up into the city at large (representing the commoners). Commoners could not vote, nor advocate for political ideals safely. But there was one Venetian social institution that did not care about class... the Scuole Grandi.
The Scuole Grandi were united by their passions for the arts, but this did not limit their influence to the arts only. Anyone could join and many lower-class citizens did, influencing those who could vote and lead in the process. Through their paintings and ideas, they could influence both the state and church towards their more liberal and open-minded ideas. The Renaissance was more than art, and the art of the Renaissance was essential to Venice's development as a city and culture. So, in a roundabout way, it was a "secret society". Mission accomplished.
Having completed our quest, Langdon thanks us for helping him on this journey, and kindly asks we deposit his walkie-talkies at the Scuole Grandi.