Thingview doesn't work for some reason here so I have reuploaded it here: https://www.thingiverse.com/thing:5530321

This is a square circle or "squircle", as in an object when viewed from one end is a square and from the exact opposite side is a circle. It is impossible to see the illusion without perspective (luckily, thingview has perspective enabled) because in isometric view, one views the object from infinitely far away, and thus you cannot change your perspective with regards to how close you are to the object; you can only zoom in.

There are two models available for printing: one with filleted edges and one without. The model with filleted edges is a faster and easier print (Square_Circle_2). If you have good bed adhesion, it is possible to print the filleted model without supports at certain sizes. Otherwise supports are needed because before the arches are completed the model is quite unstable during the print.