Considering that first riddle solutions are usually found close to the beginning of the mission I assumed that the solution can be found in a swampy area around the building I was on. After some scouting (and getting rid of patrolling enemies) I found the solution on the ground a bit northeast of the starting location.
I spent good two hours researching this riddle. Didn’t help. I thought I was looking for a graveyard, but there were no landmarks near that talked about a particular graveyard. In the end I found out on a youtube video that I am supposed to be looking for a fountain next to a big palace-like building north of the previous riddle’s solution. No way I could have put that together. Maybe I should progress through the main story mission more to get the reference? In any case, here are the screenshots to help you solve the second Gemini riddle.
I immediately thought of two rivers meeting. Looking at map I managed to see that Bièvre goes into Sienne and decided to look for an old tower there. As I was approaching the spot I saw a small tower on the corner and found the solution to the third and final Gemini riddle.
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