Büyükada is the largest of the Princes' Islands and the only one most visitors actually go to. Car-free since long before that was a virtue; pine-forested over most of its southern half; ringed by wooden mansions from the era when Istanbul's Greek, Jewish, Armenian and Levantine bourgeoisie all summered here. Six kilometres, half a day, weekday for sanity.
Arrive by ferry — ninety minutes from Eminönü on the Adalar Hattı, less from Bostancı or Kadıköy. The pier opens onto Birlik Meydanı with its clock tower; head south down Çankaya Caddesi. The first kilometre is the wooden-mansion street: bay windows, ornate verandas, the Yanaros mansion where Trotsky wrote half his autobiography in exile from 1929 to 1933.
South of the village the climb begins. The road becomes a pine-forest path; an hour at a pilgrim's pace gets you to Aya Yorgi Monastery — small, white, two hundred metres up. The terrace gives you the Sea of Marmara and the mainland skyline you came from. Pilgrims traditionally unspool a thread on the way up; do it or don't.
Walk back down the same way. Last ferry is around 8pm, sooner in winter — check the board.