Armed with a logbook, GPS and camera, Johnson walked 52.2 miles over four days, documenting everything, from the earthquake training area, which is now behind building 325, to a plastic skeleton in an elevator shaft in building 301.
When he was finished, Johnson collaborated with a team of designers to create a map for fellow JPL employees. Although some parts of the Pasadena, Calif., lab are open during public tours, many of the spots are accessible only to JPL employees. The lab does hold an open house once a year.
Here are a few of the curiosities Johnson unearthed.