The potholes of Keelung River are a world-class geographic wonder. They occur more frequently in the upper streams of the river. Potholes are formed by the strong eddies containing sand and gravel eroding the riverbed. Over time, round holes are formed, and they are called potholes. Between Houtong Station and Sandiaoling Station on the Pingxi Railway Branch in Ruifang District, as the Keelung River riverbed cuts into the hard, Nuannuan sandstone layer, there are many smooth holes on the rock surface here. They are called potholes in topography, which became the well-known sight of Keelung River potholes.
Houtong Ruifang is the most easily reachable place for seeing the potholes. From under Wengzitan Bridge outside the Visitor Center of Houtong Coal Mine Ecological Park, walk about 1,700 meters upstream along the stepped revetment, which should take about 30 minutes one-way. You will see Houtong potholes, which are called “the rock dimples“ by locals in Ruifang. You can also see the potholes by walking upstream Keelung River along Houtong Road from Houtong Station.