How do you make a 3D paper triangle?

Question

Does anyone know how to make the 3D paper triangle with just a regular 8x11 inch paper? It should look like a stage kind of but iwth a triangle shape

And not enclosed there's an opening like where yuou can write stuff in it.

Answer 1

Check these out.

http://www.korthalsaltes.com/special_pyramids.htm

Answer 2

Cut four triangles and glue them together.

Or glue three toothpicks in the shape of a triangle.
When dry, add two toothpicks to make second triangle.
When dry, add one toothpick to make third triangle.

Cut four triangles and glue them on toothpicks.