Sandfall Block

This gives you a permanent curtain of pouring sand that never actually goes anywhere. The tooltip leans on that directly, since sand dropping on your head is one of the oldest ways to die underground and this is the version that cannot hurt you.

It reads best as a vertical strip framed by something solid, the way you would run a waterfall down the back of a room. Spread flat across a wide wall the motion turns into noise.

The catch is the gate. It looks like a starter desert material and it is not one: you need a Crystal Ball set up before you can make any, so it lands in your building kit long after the theme suggests it should.