When my brother and I were in our teens, ( and that is a LONG time ago ), our mom and dad would plan a Sunday outing of some educational value. We lived in So. California, so a visit to Mt. Wilson observatory, Descancio ( sp ) Gardens, Griffith Park, were such places.
Among these was Huntington Library which includes various beautiful theme gardens. One of these was a cactus garden. This shot was taken with my very first camera, ... an Argus C3. So, IT IS MY OLDEST !
So, start digging through your files and see what you find ... show your oldest.