Wikipedia
Iljumun
Iljumun is the first gate at the entrance to many Korean Buddhist temples. Called the "One-Pillar Gate", because when viewed from the side the gate appears to be supported by a single pillar.
This symbolizes the one true path of enlightenment which supports the world. It is the boundary between the Buddhist temple and a human's worldly life. The gate symbolizes purification and one must leave all of their worldly desires before entering the temple.
The oneness is also a metaphor for non-duality (unity) in spirit and heart.
An image of an iljumun appears on the obverse of the Korean Service Medal.