This portion of the wall has been under a lake since the 1980s, but unless you planned on ferrying a few hundred pounds of diving equipment across the border, you couldn't take it on until now. Your scuba-sherpas will suit you up, bring you to the exact spot where the wall dips underwater and guide you to its most dive-worthy parts. Once submerged, you'll stumble across a few Ming-era stone carvings, some intricate tunnels and a tight-squeeze guard tower that will require every last ounce of your Bond-like scuba ability. (Wearing your backup tux is advised.)
Over the course of the trip, you'll get two scuba-assisted dives into the Atlantis-style ruins (feel free to keep the dress semi-formal for the second) before you start the earthbound portion of the voyage, which includes a guided tour of the unrestored parts of the Forbidden City, usually off-limits to tourists.
Thank you to our friends at Urbane Nomads for another great one!