The white Byzantine-style cathedral on top of Montmartre Hill. Completed in 1914, it is the best viewing point with a 360-degree panorama of Paris city. Entrance to the cathedral is free (only the dome observatory requires a fee). If you go early in the morning, you can enjoy a leisurely view of Paris without tourists.
💡
There are a lot of stairs to climb up the hill, so physical strength is required. There is also a cable car (funicular) (metro tickets available). Beware of pickpockets. Also visit the Place du Tertre, the painter's street at the bottom of the hill.