[Guest]

Three 3-sided pyramids (not counting their bases) are arranged in a triangle on a flat surface, point to point, each facing the same direction. A fourth pyramid is carefully balanced on the three. It, too, is facing the same direction, and touches the other three, point to point. The four pyramids form a larger pyramid, with a distinct void in the middle, itself forming a shape confined within the boundaries of the larger pyramid.

Describe that shape.

[bonanova]

Three 3-sided pyramids (not counting their bases) are arranged in a triangle on a flat surface, point to point, each facing the same direction. A fourth pyramid is carefully balanced on the three. It, too, is facing the same direction, and touches the other three, point to point. The four pyramids form a larger pyramid, with a distinct void in the middle, itself forming a shape confined within the boundaries of the larger pyramid.

Describe that shape.

Spoiler for #3:

The third Platonic Solid - a regular octohedron.

[Guest]

it is a 3d siripinsky's gasket

[Guest]

Spoiler for #3:

The third Platonic Solid - a regular octohedron.

Aptly said. Yes, that is correct!

By the way... got no bites on a similar puzzle... the Candlemaker. Care to have a look at it?