Hwanghae Province Haeju City
Sumi-san  Gwangjo-saji
須彌山門 廣照寺  수미산문 광조사
Ruined site of one of the "Nine Mountain Zen-Gates":
"Marchmount Meru Extensive Reflection"  Seon Monastery
Korean Master Yi-eom Jincheol Daesa 利嚴 眞澈 大師 (869-936), was certified enlightened in the
Caodong 曹洞
Seon [Chan, Zen] Lineage while studying in Tang China.  He then returned to Korea in
910 and founded the Sumi-san School of
Seon.  He eventually established Sumi-san-mun Gwangjo-sa
須彌山門 廣照寺 수미산문 광조사 Temple in what is now Geumsan-myeon District of Haeju City in
Hwanghae Province of North Korea.  Of that name, "
Sumi-san" means mythical Mt. Meru (largest and
central mountain of the world in Hinduism & Buddhism, physically identified with Mt. Kailash in Tibet)
; the -mun is "Gate",
meaning the entrance-gates of the mountain-monasteries that
Seon adepts can pass-into, not coming
out again until they are enlightened; and "Gwang Jo" means extensive/universal illumination/reflection
(as in a mirror, a reference to the classic Seon story of 6th Patriarch Huineng's enlightenment).

That was the last sect of the great
Gusan-Seonmun 구산선문 "Nine Mountains Meditational Gates"
monasteries to be established, and it did not flourish well due to the civil-wars chaos that ended the
Unified Shilla Dynasty.  That temple was finally fully founded by Taejo Wang Geon in 932, just only 4
years before Master Yi-eom died.  It was honored in early Goryeo, as the lineage continued, but all
the differing lineages ended with Bojo Jinul Guksa's "
Jogye" unification in 1200.  This temple was lost
in the mid-Joseon era -- the last record of it operating seems to be 1418. Only two stone pagodas
3-story Shilla-type and a 5-story early-Goryeo-type)
and a biseok [stele monument] for Yi-eom (erected in 937,
inscription by Choi Eun-wi, nephew of Great Sage "Go-un" Choi Chi-won)
exist on the site now.  The biseok is
named the Jincheol Daesa-bi 眞澈大師碑 진철대사비 or True-Limpid Great-Master Stele, referring to
Yi-eom's postumous title.  Because it's in a remote part of North Korea with little tourism, we don't
know much more than that.
The biseok stele recording the biography of Seon Master Yi-eom Jincheol Daesa 利嚴 眞澈 大師
and a rubbing of its inscription written by Choi Eun-wi, kept in the National Museum of (South) Korea