If you think that structures created with blocks are ephemeral and transcient, take a look at “A Sign in Space, an art installation by Gunilla Klingberg at Spain ’s Laga Beach .   ” It’s a “truck tire star pattern” that’s diligently embossed into the sand at low tide, only to be washed away at high tide. The beach becomes a giant groomed sculpture, only to turn back into unformed sand.”