The Penrose triangle
is an impossible figure which can be realized physically so that the eye gets
fooled. We featured the triangle previously in an
Exhibit from 2012
as well as in an Exam from
2013:

You can fly it:

(Recorded on September 18, 2016. The Penrose triangle.
Here
is the Mathematica file which allows export into any 3D format.
The DXF file
which can be imported into Sketchup from which one can generate
The KMZ file
which can be imported into google earth).

which can be imported into google earth).

Here are two nice Penrose triangle implementations from the
Wikipedia article.