Senko

Senko incense
Japanese love to burn incense. They use incense to relax, give a pleasant fragrance to house, and to purify the space.
Senko incense has a long tradition in Japan. It first introduced from China sometimes during the Muromachi period. Senko has roots in Chinese medicine where it was used for healing purposes, to heal the body and soul. During the Edo period, Buddhist temples started to embrace the joys of the incense. They were used for enjoyment in the temples and for religious offerings.
In Zen Buddhism senko is used to help the meditation, and to purify the mind from thought.
Neurologists say that the area of brain which produces a sense of scent is located near limbic system, the place that produces memories. Maybe that's why, when we feel scent, it often brings back memories. Lafcadio Hearn said it better than I can:
"I see rising out of darkness, a lotus in a vase. Most of the vase is invisible; but I know that it is bronze, and that its glimpsing handles are bodies of dragons. Only the lotus is fully illuminated: three pure white flowers, and five great leaves of gold and green,-- gold above, green on the up curling under-surface, an artificial lotus. It is bathed by a slanting stream of sunshine; -- the darkness beneath and beyond is the dusk of a temple-chamber. I do not see the opening through which the radiance pours; but I am aware that it is a small window shaped in the outline-form of a temple bell. The reason that I see the lotus -- one memory of my first visit to a Buddhist sanctuary--is that there has come to me an odor of incense. Often when I smell incense, this vision defines; and usually thereafter other sensations of my first day in Japan revive in swift succession with almost pain acuteness."
In Japan, one might see students in temples exercising a peculiar custom, they take their hats off and try to attract the smoke to their hair - a custom which is believed to help concentration in school.

Different types of casual incense okou
But senko really has pleasant scent. The casual type of senko, which is for only enjoyment (not for religious & professional use) is called okou. Senko word itself refers to the insence related to Buddhism. Okou are available in great variety.
There is incense made from cypress, cedar, of course sakura. Some people have "incense libraries", enormous collections of different types of okou. Okou is naturally a top in the souvenir list of Japanese tourists visiting Hawaii or other Asian country.
When buying incense, sometimes the box has a small square stone with a hole on middle. One can place the senko to it. There is also cone shaped incense which produces more scent in shorter time.
In front of Japanese home altars, there is often a small box filled with fine sand. This is used for burning senko in front of the altar.
Shikibu Murasaki is perhaps most famous senko fan. In Tale of Monogatari she wrote in "Plum Branch Chapter" about incense contests and perfume creation. In the old times, sleeves of kimonos were also scented over night by exotic incense.
Japanese incense ceremony, kodo, doesn't involve burning wood, but rather appreciating it's scent in it's original form.