Ying's place is just at the station Réaumur – Sébastopol (Line 4)as described. Very convenient to buy grocery, eat in the restaurant, approach to the public transportation or access to the main sightseeing spots. Ying responses to my message very rapidly all the time which gives you a sense of security. There are stairs you need to climb, as described, so make sure you are okay with it. Thanks Ying for the help through my trip to Paris this time.