Each year, there are several official holidays that are set by the government. These have been changing throughout the years, with the biggest changed probably happening after WW2.
Some holidays are rather new, like the Vernal Equinox Day (春分の日 Shunbun no Hi) around March 20 (established after WW2) or the Marine Day (海の日 Umi no Hi) a holiday since 1996.
Some dates of holidays are kept, but names have changed, like April 29, which uses to be the Emperor’s Birthday until 1988 and has changed to “Showa Day” in 2007.
There is the famous Golden Week, often abbreviated to GW. It is a period of holidays at the end of April through the beginning of May, having the following public holidays:
April 29 Shōwa Day (昭和の日 Syowa no Hi)
May 3 Constitution Memorial Day (憲法記念日 Kenpō Kinenbi)
May 4 Greenery Day (みどりの日 Midori no Hi)
May 5 Children’s Day (こどもの日 Kodomo no Hi)
These days are public holidays and the average employee does not work on them. Some, who are considered to be lucky, take the in-between weekdays off as well to form a real holiday week, the complete Golden Week!
In 2015, on had to take April 30 and May 1st off in order to have one entire week off.
This week is similar to the Obon-holidays and domestic tourism reaches it’s peak with airports being over-crowded, main stations having delays, hotels booked out and the available ones charge horrendous fees, shopping malls and department stores are crowded with people, usually pushed by special Golden Week Sales campaigns and the average sightseeing spot is having even more visitors than usually.
If you want a peace of mind, travelling during the Golden Week is not recommended, so try to just shift your vacation a week earlier or later and you can experience a more stress-free travelling!