Located north of the COEX Mall near the World Trade Center, this temple was founded in much quieter times -- A.D. 794, during the Shilla Period. One of the Seon (Zen) centers during the Joseon Dynasty, it was originally called Gyeongseongsa (which means "seeing true nature"). It fell into decline during the Goryeo dynasty, but was renovated and given its present name in 1498. The oldest building still standing was built in 1856 and houses the 150-year-old wooden blocks of the Avatamsaka Sutra (called the "Flower Garland" or "Flower Adornment" Sutra in English), as well as other sutras (Buddhist scriptures). At 4:10am and 6:40pm daily, the monks play the four percussion instruments to awaken the four heavenly beings of the earth, sky, water, and underground. Since it's one of the few South Korean temples to be located in the middle of a city, weekends are positively crawling with worshipers and visitors. The best time to visit is during the early-morning percussion ceremony to hear the echoes of the gongs before the city awakens.
English-speaking guides are available 9am to noon and 1 to 6pm on weekdays. You can also do an overnight temple stay (for a recommended donation of W50,000-W80,000) or just take a 2-hour tour of the grounds. If you're visiting in the fall, don't miss the Jeongdaebulsa ceremony held on the ninth day of the ninth lunar month, when the monks carry scriptures on their heads and recite the Beopseongge (Buddhist rites).