(I also managed to crash the thing, but that's not the point of this post.) These microscopes take really fantastic pictures down to really tiny sizes. This size of this crevasse is about the diameter of a human hair.
You could have easily seen this in an optical microscope, some of which can see things (if you push it) even 100 times smaller than this hole. However, the SEM can see things 100 times smaller than that. To get a sense of this, here's a serious of pictures I took using the SEM. Each picture has a red box around what you see in the next zoom level:
The whole picture is around 2 mm across and each of the squares in the image are about 2 times the diameter of a human hair. Now, we zoom in on one of the squares:
And now further towards that speck in the middle of the picture:
That canyon is about the size of a water droplet in fog. Let's zoom in a bit more:
And a tad more:
This image approaches the limit of optical microscopy. An old-school microscope image of this would not be anywhere near as sharp. For example, if you click on the picture to make it bigger you'll see that the bright stripes are actually made of a bunch of little blobs (gold nanoparticles, I believe). You would certainly not be able to see that optically. And now, we'll zoom in some more:
The larger blobs are about the size of the wavelength of ultraviolet light. And now we'll zoom in once more:
The big blobs in the center of the screen are about the size of the thickness of a cell membrane, about 10 nm. As a sense of scale, if those big blobs were peas, an actual pea would be around the size of the Earth. The teeny little dots on the left are around 1nm in diameter (the maximal resolution of this SEM). As a further note of scale, if we were able to zoom in on this picture as much as we have from our first picture (and we can't) we'd be seeing atomic nuclei.
Any thing you'd like to see electron microscoped? The guy who trained me suggested starting a bug collection.