A labyrinth, a unicursal path with windings leading you always to the middle and back.
If you want to know more about labyrinths here is a link:
http://www.heartphone.net/?lang=en

Constructed this labyrinth with 3D blocks (squaring the circle) in 3D GameStudio. Exported it from native Prefab to 3DS. With the student version of Adobe CC created a solid STL file.