The two-bedroom penthouse comes with sweeping views of the Eiffel Tower and just about every other monument across the Paris skyline. The rent, at 600 euros a month, is a steal.

Marine Vallery-Radot, 51, the apartment’s tenant, said she cried when she got the call last summer that hers was among 253 lower-income families chosen for a spot in the l’Îlot Saint-Germain, a new public-housing complex a short walk from the Musée d’Orsay, the National Assembly and Napoleon’s tomb.

“We were very lucky to get this place,” said Ms. Vallery-Radot, a single mother who lives here with her 12-year-old son, as she gazed out of bedroom windows overlooking the Latin Quarter. “This is what I see when I wake up.”