At Gumunso in Taebaek, a river appears to pass through a stone gateway in the mountains. The place name combines an old Korean word for a hole or cave with a word for a deep pool. Hwangjicheon and Cheoramcheon meet here, where water erosion and geological change shaped the unusual rock passage.
The official Taebaek Paleozoic Museum explanation describes limestones, dolostones, shale and sandstone formed in an ancient marine environment. Ripple marks and other sedimentary traces, along with fossils of marine creatures, help visitors imagine a landscape very different from today's mountains. The museum also identifies the area's Paleozoic beds and river-eroded landforms as a protected natural-heritage site historically designated Natural Monument No. 417.
At the riverside, look for layers and patterns in the rock without damaging them. The nearby Taebaek Paleozoic Museum offers a wider context for geological time and the evolution of life. The geological article itself does not verify whether every outdoor path is currently accessible or provide live museum admission, closure and transport details. Recheck these before travelling, keep clear of unsafe riverbanks and do not collect rocks or fossils.