Girls wash their hair in sweet flag water during an event celebrating Dano at the Korean Folk Village in Yongin, Gyeonggi Province on Sunday. /Newsis

Sunday was Dano, one of the oldest traditional feast days in the lunar calendar in Korea when the energy of yang is strongest.

In the philosophy of yin and yang, odd numbers are yang, and even numbers yin. The days when the day and month are matching odd numbers -- for example the third day of the third month -- used to be considered as auspicious dates, and May 5 in the lunar calendar used to be regarded as the most auspicious day as the power of yang reached its peak.

Various folk events are performed on Dano, washing hair with water infused with sweet flags, chasing away bad spirits by wearing new clothes, women playing on swings, mask dances, and a kind of wrestling.

There is a saying, "There is no plant that cannot be eaten on Dano in May," meaning all plants nurtured with the spirit of yang are healthy.