The Craziest Things You Can Do On A Cruise Ship

While zip lining on your vacation may not seem like a big deal, doing it on a cruise ship may be – especially when the zip line is 10 decks high. Symphony of the seas' zip line dangles above the ship's boardwalk, not open sea, which isn't quite as terrifying but still offers some impressive views. The zip line is included in the cost of the cruise and no reservation is required, so it doesn't have to be a once-in-a-lifetime (or even a once-in-a-cruise) experience.