<p>“Impossible objects” were first introduced through 2D illustrations known as “impossible figures”, and were later realized as physical 3D objects using specific techniques. These objects create optical illusions that produce a sense of impossibility when viewed from specific viewpoints. In this paper, we propose a variant of impossible objects that people can physically engage with rather than just observe. We introduce two examples: First, a walkable large-scale 3D model of an endless loop of stairs, where walking strengthens the sense of impossibility. Second, a set of “antigravity” snow slopes that appear to allow sleds to slide uphill. In the second case, the slopes themselves look normal, but the motion of the sleds creates the sense of impossibility. We show the design principles as well as actual implementations, and discuss the potential of the impossible objects as playground equipment and entertainment resources.</p>