Possibly the most visually impressive aspect of Jeongwol Daeboreum is the creation of large hillside fires in observance of 'Rat Day'. The point of these fires was to drive away rats and other pests that would otherwise make their home in fallow fields, although on Jeju Island this event has become more of a tourist activity than an agricultural practice in recent years. With a date determined by the sheng xiao, this year's event in Jeju-do took place between 26-28 February on the volcanic remains of Saebyeol Oreum -- rather fittingly, the locale's name comes from the expression "it brightens like a star".
The image at the top of this entry comes from the jeju.tistory.com website and you can see several more images from last year by following the link to their site. Don't forget to click on the images to see a larger-sized view. It may also be worth checking out this page for more on this year's event in Jeju.
Smaller fires are created through burning daljip (달집; 'moon shelters' or 'moon houses'). Seasonal Customs of Korea explains:
The burning of "moon shelters" was also observed on the night of the full moon. While waiting to "greet the moon", youths would build a cone-shaped mound of green pine branches or bamboo with an opening facing east, the direction from which the moon rises. A moon-shaped figure was hung inside and when the moon arose, the moon shelter was set ablaze [...] it was said that the village would enjoy a year of abundance only if the smoke from their moon shelter rose higher than that of nearby villages.
Like the Jeju-do 'rat fire' it's still possible to see burning moon shelters in contemporary Korea. Some images from the past couple of days:
Busan 달집 before being set ablaze. Source.
Busan 달집 after being set ablaze. Source.
Unknown location. 달집 with folk musicians (풍물) on the left. Source
Unknown location. 달집 and shaman (무당). Set of large-size, good-quality photos available here.
달집 tree. This photo also offers a view of Korean kites (연) and the slips of paper tied to the 달집 with one's wishes for the new year. Source.
One other Daeboreum activity from Jeju-do is horse fighting -- facing two horses against each other -- though it's not a topic I had planned to write about tonight. There's some information available (in Korean) here, here, and here. I haven't read any of it though, so can't confirm the accuracy of any information on those sites (or guarantee a neutral point of view).
말사랑 싸움놀이 Source.