Tongpanyu is 6 nautical miles off the coast of Magong Island; the entire island is surrounded by columnar basalts of clear lines, the columnar joints is the most enriched in Penghu, and has long been known as the "Yellowstone Park of Penghu".

The columnar joints and platy joints on this island are all very well-developed; originally a hexagon or pentangle, the rock columns are now pretty much circular on the edges due to the fierce weathering and erosion, the color has also faded due to oxidation, some tip of the columnar basalt have already been weathered into a ball shape.

The abrasion platform on the southwest coast of Tongpan has a concentric circles platform formed by the basalt lava, called the "lotus platform"