When we think of outdoor sculptures, towering monuments and intricate statues often come to mind. But some of the most fascinating works of art are those you can't see at all—conceptual pieces that challenge perception and redefine public art.

One notable example is "The Invisible Sculpture" by Italian artist Salvatore Garau. In 2021, he "installed" an invisible sculpture in Piazza della Scala, Milan, complete with an auction price tag. The piece exists purely in the viewer's imagination, inviting contemplation about the nature of art and space.

Another intriguing work is "Air Art" by Yves Klein, who famously patented his own shade of blue (International Klein Blue). His invisible sculptures consist of empty spaces where he declared the presence of "immaterial pictorial sensibility," leaving only a certificate of authenticity as proof.

In Japan, artist Jeppe Hein's "Invisible Labyrinth" uses GPS technology to create an unseen maze. Visitors wear special headphones that guide them through an invisible structure, blending physical movement with digital art.

These works remind us that art isn't always about what we see—sometimes, it's about what we feel, imagine, or experience beyond the visible world. From optical illusions to pure conceptualism, invisible sculptures continue to push boundaries in public art.

Would you walk through an invisible maze or bid on empty space? These thought-provoking pieces prove that sometimes, the most powerful art is the kind you can't even see.