A <a href="https://en.wikipedia.org/wiki/Reuleaux_tetrahedron" class="extiw" title="w:Reuleaux tetrahedron">Reuleaux tetrahedron</a> enclosing its regular <a href="https://en.wikipedia.org/wiki/tetrahedron" class="extiw" title="w:tetrahedron">tetrahedron</a>. Made in <a href="https://en.wikipedia.org/wiki/Blender_(software)" class="extiw" title="w:Blender (software)">Blender</a>.
<a href="//commons.wikimedia.org/w/index.php?title=User:Quadduc&amp;action=edit&amp;redlink=1" class="new" title="User:Quadduc (page does not exist)">Stian Ellingsen</a>
CC BY 2.5
<span class="int-own-work" lang="en">Own work</span>