Gokayama is famous for its farmhouses, which are built in a unique architectural style known as gasshō (合掌). The name means "hands together" as in prayer, referring to the steep roofs that keep the snow off in the winter. Underneath the roofs, the large attic area was used to house silkworms.
The kanji of the current name mean "Five Mountains", but the original name is actually "Between Five Valleys" (五箇谷間), which is pronounced the same.
Gokayama is somewhat inaccessible. The nearest city of any size is Takaoka, from where you can take the JR Jōhana Line to its terminus Jōhana (50 min). From here, Kaetsunō buses  travel to Gokayama (40 min). It's also possible to take buses direct from Takaoka, but this costs more (¥1,800) and takes longer (2 hours).
Gokayama offers numerous ryokan based Japanese inns for overnight stays. Most of these inns are gassho based inns and offer both dinner and breakfast in the accommodation fee. Dinner is generally traditional Japanese dishes consisting of river fish and exquisite mountain vegetables; you will almost certainly sleep on a futon on a tatami mat.
Just like the better known Shirakawa-go, Gokayama's buildings are mainly produced of highly flammable traditional materials, smoking is heavily regulated in the village. If one must smoke they must do so at a designated position within the village (indicated by bench seats, a sign and a 3 foot high large ash tray). Please refrain from smoking unless in a designated area. Gokayama has a backup village fire suppression system, however, triggering it via a burning cigarette butt would be a foul end to a good holiday.
Although this is a moderately popular tourist destination, some people do live in some of the traditional houses. Keep this in mind as you tour.