What kind of secrets can the Freemasons possibly have?

People got interested in freemasonry after reading too many Dan Brown books, I get it – I get that it’s a society with secrets – but what possible secrets/knowledge could they have..I mean really? Long ago, different mason societies had architectural tricks up their sleeve that they didn’t want others to know about and given the times, this was probably relevant…but now? Maybe I’m missing something but there is no such thing as some sort of secret truth that retired middle to upper class white guys with fun robes and clubs with crests on the doors have that we, people on Fluther, do not…