The Petit Trianon is a small neoclassical palace — four floors, essentially a cube — built between 1762 and 1768 for Louis XV's mistress Madame de Pompadour, who died before it was finished. Louis XVI gave it to Marie Antoinette in 1774 on the first day of his reign, and she made it the centre of her private world for the next 15 years.
The interior was refurnished by Marie Antoinette in a light, elegant style — pale walls, delicate gilding, mechanical furniture that could be raised and lowered through the floor so servants were not needed. The building was her retreat from the crushing formality of the main palace, where she had almost no privacy, where every act of dressing and undressing was watched by dozens of courtiers. At the Petit Trianon, she could at least choose who was admitted.
The English-style gardens she created around it — with artificial hills, a lake, winding paths, and a temple of love on an island — are still there and still pleasant. The contrast with Le Nôtre's geometry 500 metres away is striking.