Build a mini-sandcastle at the beach or in a sandbox.

“About 15 years ago I went to visit a friend of mine who was living in Florida at the time. We spent one day at the beach and I decided to build a sandcastle, as a full grown adult, because I could. I spent half an hour or so building the castle at the water's edge. Then I took a couple of pictures of it as the sun was setting and forgot about it. A few weeks later I uploaded some images from my trip to Flickr, and posted the general location of some of them. Flickr came up with some list of photos taken nearby, and it actually showed me a few pictures of my own sandcastle, taken at different angles. It was unmistakably the same sandcastle I built. Someone else took some pictures of my sandcastle and posted them to Flickr before me.”