The Dongtian Waterfall (洞天瀑布 [Dòngtiān Pùbù]; Heaven Cave Waterfall?) was a confined slot canyon waterfall that was difficult to photograph since it was essentially a waterfall squeezed inside of a slot canyon (quite like the Cleddau River rushing through the Chasm on the way to Milford Sound in New Zealand). Even though it was not the most photogenic waterfall, Julie and I certainly appreciated the noise from the power and turbulence of the waters within.
Further downstream, the river fell and cascaded into the Underground Forest. The waterfall right at the edge of the depressed forest was more photogenic than the Dongtian Waterfall. In any case, it was said that an earthquake (probably related to the volcanic activity here) had split up the hillside in a big fault. Today, that fault was now filled with trees as well as the newly created drainage in which the Underground Forest Waterfall spilled right into. The steep cliffs surrounding the forest attested to the geological oddity that gave rise to this scene.
When we did this excursion taking in both waterfalls, it took us 2 hours to do the walking plus taking photographs. The walk was on mostly flat boardwalk towered over by tall trees. The difficulty rating reflected our experience of extending our visit to both waterfalls.
There's a bus stop between the main intersection (where there are hotels as well as shuttles to both Heaven Lake and the Changbai Waterfall) and the park entrance. From this stop, you have to walk some 2km each way I believe to get to the Underground Forest. A separate spur path for a few hundred meters branches off and goes to the Dongtian Waterfall.
To give you some more geographical context, Dunhua was 193km (3 hours drive) southwest of Mudanjiang, 1,274km (13 hours drive) from Beijing, and 295km (4 hours drive) west of Jilin.
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