What a fantastic little hideaway, only blocks from some of the left bank's (the Seine's southern bank) best sites! Within a 10 minute walk, you can find yourself in two of Paris's great public gardens (Luxembourg and the Jardin des plantes), or at the Pantheon (worth doing the rooftop visit!), the Sorbonne, or the Catacombs. Oh, and the food... with easy access to several top-rated restos, cheese shops and bakeries, you can't go wrong. My advice, however: avoid the touristy areas and go one or two blocks out of the way to find better cuisine and shopping. This is one of Paris's most historic districts, and you can experience it from a more modern building with good amenities and lots of space for a family (we had five staying comfortably). Even during a heatwave of 35C during the day, the air flow through the apartment cooled us down at night and we were incredibly comfortable.
Ludovic and Brigitte were great at communicating with us in advance and during the visit, sending us a guidebook, a text message ahead of time, and other little courtesies that made it easy to message them. The building is very secure and very soundproof - the normal noises of a big city couldn't penetrate the courtyard where the apartment is located.
Lastly, a word of advice to travelers: if you are visiting in August, remember that a lot of Paris shops close down for summer vacations! Museums and tourist areas are always open, but restaurants may not be even if Google lists them as open. There's plenty of things to see, do and eat nearby, but you may have to wander a little. Paris is at least a city that rewards wandering, and Ludovic's apartment is a great place to do that from!