Although City on the Edge of Forever is one of my personal favorites, a couple other episodes come to mind- For the World is Hollow and I Have Touched the Sky and All of Our Yesterdays.
2
Besides, we always seem too busy with our todays to do much looking back to yesterdays.
3
His volumes of reminiscence, Cheerful Yesterdays (1898), Old Cambridge (1899), Contemporaries (1899), and Part of a Man's Life (1905), are characteristic and charming works.