The flat torus embedded in 4D, projected via stereographic map
The Clifford torus is a flat (zero intrinsic curvature) torus embedded in the 3-sphere S³ ⊂ ℝ⁴. It lives in 4D as {(cos θ, sin θ, cos φ, sin φ)/√2}. When projected by stereographic projection from S³ to ℝ³, it becomes the familiar donut shape — yet in 4D it is perfectly flat. It is a fundamental object in the Hopf fibration.