I don't know what being a Gemini has to do with it, but if he enjoys the outdoors, then yes zip lining would be something fun to do outside, or whitewater rafting if you have that around you.
What would be a fun date to suggest to a Gemini man? I was thinking we should go zip lining, but that's my opinion.
I never go by them horoscopes on who to date, I go by the person and their personality but if you meet someone whose got something compatible it does help out but then others say opposites attract, so hard to say...