Today is the first day of a long weekend in Japan because Monday is a public holiday called 海の日（うみのひ）, “Marine Day.”
This is the second newest public holiday in Japan that became effective in 1996. Originally it was 20 July but since 2003 it has been observed on the third Monday of July so that people can enjoy a long weekend. And apparently it will be observed on Thursday 23 July in 2020, which is the day before the opening ceremony of the Tokyo Olympics.
Since 海の日 is still new, there aren’t many set events on the day but this is the first public holiday since the end of the Golden Week in May, this 三連休（さんれんきゅう）has been welcomed by most people.
If you are in Japan working, enjoy your long weekend!