My cousins who lived nearby had an amazingly ornate cardboard fort that their parents bought for them at Sears. It was setup in their finished basement and once I played in it, I would not shut up about how awesome it was. A few months later my sisters and Mother surprised me with a cardboard clubhouse of my very own that they had picked up at a garage sale. They set it up in our unfinished basement and it was amazing. I would sit down there for hours.
A few months later the basement flooded and my cardboard fortress of solitude was reduced to a pile of wet mush. I believe I wept quietly as I carried it piece by piece to the trash.
A few week later I tried to recreate it using boxes and tape, but I lacked the aptitude for cardboard construction and eventually gave up on the dream. Which is probably good, because the basement flooded again the next year when a pipe broke and I do not think I could deal with the loss again. Still, like everything else, the memories remain.