I live in the U.S. When I went to Korea in 2016 to present at a conference, I asked the organizer about sites related to King Sejong the Great. He only knew of the famous statue in Seoul.
I was more interested in any historical site related to King Sejong's daring program to create a Korean alphabet - designed so that any farmer could learn it in a day. I had read how, to avoid backlash from the dominant Chinese, King Sejong had sequestered a team of scholars in a "hidden laboratory" at a now unknown location in Korea. The team worked for over a year to create a simple, phonetic alphabet with the potential to create universal literacy. I loved this story, but had no hope of visiting any sites related to it.
My next highest priority was to visit a Buddhist temple. The organizer recommended Jingwansa, and arranged an overnight stay for a small group of us from the conference.
Shortly after we arrived, a volunteer gave us a talk about the monastery and its history. To my amazement, she told us this story:
Most of the buildings were destroyed during the Japanese occupation during WWII. When people finally went to rebuild on the site of one of the demolished temple buildings, they discovered some very old papers. Eventually, some scholars were able to recognize these papers as indicating that this temple was the site of King Sejong's "secret laboratory"!
One piece of evidence supporting this theory, the volunteer said, was that whenever the Korean government built a significant building in those days, they would plant a Ginkgo tree in front of it. Sure enough, there is an ancient Ginkgo tree standing in front of one of the temple buildings!
I can't verify the accuracy of the volunteer's story, but I feel privileged to have stood at the foot of a tree that may perhaps have been planted at the direction of the visionary king, King Sejong!