Heritage day in Paris

This year, September 19 and 20 mark the 26th anniversary of Heritage Weekend. This special event is celebrated in France and throughout Europe (49 European countries, I hesitated in writing this figure down.. I do not know how they count 49 countries in Europe!)- and even in Uruguay, I hear.
It started in Paris in 1984 when the Historical Monuments opened many "private" monuments to the public; it became a tradition and for years it was the third Sunday of September. It is now a whole weekend that the event lasts!
Thus every year the government opens to the public (free of charge) 15 thousand monuments, buildings, places that are usually not open for visits. Some years, even the Elysee Palace, the presidential building, has been open. Many foreign embassies housed in old and remarkable buildings also open their doors to the public. Last year there were 12 million visitors!
Nevertheless, Saturday evening I was surprised to find at Porte d'Auteuil, my metro station, as I was stepping out of my train, a beautiful old metro. I did not think right away about Heritage Day, but learned later (thank you Google) that the Paris Metro Company (RATP) had brought to my metro station several carriages of the very first metros for everybody to enjoy on Heritage Day. The Paris metro is over 100 years old.
Long gone are the days of these wood classy metros. In the old times and up to the early eighties there used to be a first class (the red one) and a second class (the green one). The first class carriages had leather seats and because 1st class tickets were more expensive, it was less crowded. Typically there was one first class carriage in the middle, and four 2nd class, two on each side. Nowadays, 10 000 000 people a day take Paris public transportation, which is effective, safe, and reliable!!
Do you have a Heritage Day in your country?