While I think the electric gym is more likely than this, I'm not discounting the possibility that Lumiose City might have the grass gym.
Remember in the early trailer that the trainer was shown climbing an artificial tree on a metal walkway via rope swings, and that's widely believed to be a gym. I haven't seen any other tall structures that would fit that as yet, plus I think it would just be plain cool to climb the Eiffel Tower using ivy, vines and rope wings. What with the presence of Gogoat in the city, I could definitely see the leader having one as their signature pokemon.
Remember in the early trailer that the trainer was shown climbing an artificial tree on a metal walkway via rope swings, and that's widely believed to be a gym. I haven't seen any other tall structures that would fit that as yet, plus I think it would just be plain cool to climb the Eiffel Tower using ivy, vines and rope wings. What with the presence of Gogoat in the city, I could definitely see the leader having one as their signature pokemon.