Not all photography is as simple as squinting into the viewfinder and pushing the clicky shutter button. Enter the world of alternative photographic processes, and take a look at this, one of my favorite little monsters...
The paper negative is an analog photographic technique which involves replacing the usual film with photographic printing paper. Roll-film formats are sometimes used, but most work is done with large-format cameras, which normally use sheet film. The larger sheets of paper are much easier to work with. In general, paper negative photography utilizes only black and white papers, although it is possible (but more complicated) to use color printing papers as well.
The paper negative process was developed by William Talbot in the 1830s. His process, the calotype, was the first by which many positives (prints) could be made from a single original negative. Although the materials and some of the methods have changed, the basic process remains the same: expose a sheet of paper coated with silver halide emulsion; chemically develop the image, producing a negative; expose a second sheet of paper by placing the negative on top and shining a light through; chemically develop the positive on the second sheet. Repeat as necessary.
Modern paper negatives are used by those experimenting with pinhole cameras and those who wish to capitalize on the medium's limitations--and therefore expressive potential. Good paper negatives are a challenge to produce: the emulsions have very limited exposure latitude and tend to be extremely contrasty.
Further, paper emulsions are pretty insensitive to light, and usually sensitive to green and/or blue light, so exposures tend to be long, even with normal-aperture lenses. Use a pinhole in place of the lens, and you're going to be there a while. Reciprocity failure usually extends exposure time even further. Indoors, under tungsten lighting, exposure time may be several hours, mainly because of the general dimness of the lights and their low color temperature.
What attracts photographers to paper negatives? Well, they're cheaper than sheet film; have characteristic limitations which can be exploited for artistic effect; and, well, for being so simple, they're a challenge to master. Plus, there's lots of room for experimentation, both in exposure and chemical process. And finally, it's satisfying to hang up a nice photograph you went through hell to make.