A huge holographic installation in a desert somewhere.
This is based on (essentially a recreation of) a scene from the film ‘Time Bandits’.
In one scene of the film, the Time Bandits find themselves in a desert and come across an invisible barrier they can’t pass through. They start arguing and one of them picks up a nearby skull from a deceased animal (maybe human, I need to check) and throws it at the person they’re arguing with.
The skull misses the person and smashes through the invisible barrier, shattering it like a massive piece of glass, and making a huge hole in it, which reveals The Fortress of Ultimate Darkness (a scary castle) behind.
This sculpture/installation would be a massive glass hologram in the desert, in the shape of a huge broken sheet of glass, with an image of a scary fortress/castle in it.