Did you know Penghu has a national marine park? South Penghu Marine National Park includes four islands–– Dongji, Xiji, Dongyuping, and Xiyuping––and surrounding isles, reefs, and ocean waters. The area is sparsely populated, so the environment is in its pristine, primeval state. The park is a popular destination for eco-tourism.

The easternmost island of Donji is the largest of the four southern islands. It’s also the point in Penghu nearest to Taiwan and was once a transshipping station between Taiwan and Penghu. Eddying undercurrents in the nearby water often caused ships to run aground on shoals and sink. Because it was so dangerous, people called that part of the sea "black water ditch.” To ensure safe navigation, two lighthouses were erected in Penghu during the Japanese occupation. Dongji Lighthouse, the northernmost is the tallest in Dongjiyu.  The black and white tower is a spectacular sight. Japanese troops were stationed on the northeast cape. You can still see the ruins of an artillery unit’s barracks; locals call them "soldier houses.”

If you go west from the tourist service center to Bagua Mountain, you can see Dongji Pier, Dongji Lighthouse and the seascape from the summit. Bagua Mountain’s rock strata is composed of long, narrow pieces of basalt. “Dongji’s Eye,” a rock formation on the mountain's left side, bears a striking resemblance to a human eye. Most of the coastline is bounded by steep columnar basalt cliffs. There’s an enormous marine erosion platform on the northeast cape locals call “the big terrace” You’ll see lots of intertidal creatures there at low tide. Donjiyu, Xiji, Toujin, and Tiezhen have been officially designated as the "Penghu South Sea Basalt Nature Reserve,” enshrining the islands’ wealth of scenic basalt landscapes.