Retrospection is the action of looking back or reviewing events and situations of the past, particularly those in our own lives. It also means to indulge or engage in retrospect. Eg, looking at my wedding photos provides happy periods of retrospection.
Retrospect means a a survey of past times or events, or to reflect on the past. Eg, in retrospect I'm glad I enrolled in creative writing evening classes fourteen years ago.
Oooh, the past is when castles were built! (It's almost like I plan this stuff.) Do you recognise this one? Or the handsome photographer ahead of me?