To access Rachel Cusk’s apartment in Paris, on the top floor of a narrow residential building in the Marais, you must first climb five flights of winding stairs. Once inside her place, you are confronted with yet another staircase, at the top of which runs a sleek corridor of rooms and a highly Instagrammable reading nook. From that level, there remains a final, minimal set of steps leading up to a loftlike living space, which gives way to a lovely terrace with unobstructed views that more than justify the effort needed to get there.