My favorite photospot of Seoul is the view from Bukcheon Hanok Village to Namsan Mountain. I must admit that "secret" is kind of clickbait as it is right next to the most famous main street of the village.. But I saw endless people walking up the famous part but not checking the streets next to it, so I wanted to add this as a separate recommendation. Hanok roofs, the little Korean Flag of a Hanok guesthouse, this overall scenic alley and the N Seoul Tower in the background. If you're lucky you can take pictures without many tourists sometimes even in the afternoon!