The Golden Week is a collection of four national holidays within seven days. In combination with well placed weekends, the Golden Week becomes one of Japan's three busiest holiday seasons, besides New Year and the Obon week (July/August)
The national holidays making up the Golden Week are:
April 29
Green Day (Midori no hi):
April 29 used to be the birthday of Emperor Showa who died in the year 1989. After his death, the day was changed into a national holiday for environment and nature since the emperor loved nature.
May 3
Constitution Day (Kenpo kinenbi):
On this day in 1947, the new post war constitution was put into effect.
May 4
"Between Day" (Kokumin no kyujitsu):
A recently introduced, national holiday to make the Golden Week a continuous holiday.
May 5
Children's Day (Kodomo no hi):
The Boy's Festival (Tango no Sekku) is celebrated on this day. Families pray for the health and future success of their sons by hanging up carp streamers and displaying samurai dolls, both symbolizing strength, power and success in life. The Girl's Festival, by the way, is celebrated on March 3.
More information about this holiday period can be found at http://www.japan-guide.com/e/e2282