Japan has a holiday period called "Obon" (Bon festival)."

This period is like a national holiday (But not nationally designated) that occurred from long ago because of day when families gathered in their hometown for religious events that originally to worship the spirits of their ancestors. However, these day it is settled down simply as a summer vacation even without Buddhist customs consciousness.

As Summer Holiday (It is not marked to the calendar in Japan),

Many companies and offices take a several days off during this period(around 10th - 18th).

Plus "Mountain Day"

A remarkable thing is that the new National Holiday named "Mountain Day" is held on 11th of August. It is marked by red on Japanese calendars, as a first-class national holiday.
Therefore many company may start their holiday from 11th and close longer than ever before.

Transportation condition

Foreign Travelers!
Take notice that a rush of Japanese travelers every year during this period occurs because they head for their hometowns and traveling destinations. So roads, train stations and airports are awfully congested all over Japan.

More about “Obon” as Bon Festival.

Japanese get used to calling it "Obon" rather than "Bon".
This is originally a Buddhist event to hold a memorial service to the spirits of ancestors about the middle of August (mainly 13th to 16th).

The ritual begins with "Mukae-bi"(Welcome fire).

Because the spirits of the ancestors are said to return home at this period, fires at the entrance to homes are lit for that the spirits do not lose their way, and, in addition to lanterns being lit inside homes, vegetables and fruits are set out as offerings.

"Okuri-bi" (Farewell fire) at evening on 16th,

Obon is over, the spirits are sent. This is called "Okuri-bi" (Farewell fire) and fires at the entrance of homes are lit again for seeing off. And in some regions, "Toro Nagashi" (which is also referred to as "Shoro Nagashi") is also a ritual where people hold a memorial service to send back the spirits by floating paper lanterns in a river or the sea.
At Kyoto, "Gonzan-no-Okuribi" is the way for sending back.
Go for the Page of "Gonzan-no-Okuribi"