17 years ago I went to a summer vacation with my family (still a teenager). That meant 10 days without any internet connectivity. I just got my first laptop and I was allowed to take it with me. I was reverse engineering MSN Messenger's user to user and profile picture exchange protocol from TCP dumps. MSN Messenger did not use any encryption. Before I went to the vacation I recorded a bunch of sessions with Wireshark (maybe it was still Ethereal back then). Then for 10 days I was just trying to figure out from the dumps how the binary protocol worked and was writing the code without any way to test it. When I came back I just had to fix some minor bugs and it worked. Fun times.