This hourglass is built of spheres, tori, cylinders and a cone in POV-Ray. These pictures are rendered in the plain enviroment of a checkered floor, but I am planning to include the hourglass in a more interesting scene.
Here is a view from inside the hourglass.
There is an older buggy version of the hourglass as an QuickTime VR object (approx. 260 KB). There are nine vertical tilt angles in it. Use your mouse to turn the object for viewing from different angles.
After combining 324 rendered frames, I realized the object would have been 1 MB (using the same compression as in these versions) to download. I figured out a way using only 81 frames. When turning the hourglass around the y axis, it look almost the same after 90 degrees of rotation. With using non-standard settings the file size is reduced to about 260 KB without easily noticable difference.
Here is an animation of the camera flying through the hourglass (in the WebM format):