At some point in the last few decades, someone took a poster and stuffed it in an unused office at Lawrence Livermore National Labs (LLNL). The poster was made by the W.M Welch Scientific Company in 1944, and it depicts in excruciatingly awesome detail how electromagnetic waves work.
Each section of the spectrum corresponds to a color-coded section in the bottom area. You can learn all about the properties, uses, and effects of each type of electromagnetic wave. It covers everything from simple diffraction to the effects of cosmic rays.
You can check it out on the LLNL Flickr page and zoom way in – its resolution is 10,000 x 6958 pixels and it’s a 107MB jpeg file.