In Arxan, Tianchi is a must-see. It isn't as showy as famous mountains and great rivers, but it holds the Greater Khingan Range's purest stillness and mystery.

This is a maar lake left by a volcanic eruption 200,000 years ago, at an elevation of 1,332.3 meters—China's third-highest crater lake.

Climb the 998 wooden steps—not steep, with larch forest the whole way—and you'll reach the top in about 40 minutes. The viewing platform at the summit is unobstructed, with the entire lake spread out below you—not a shoreline seen from the side, but the whole crater viewed from directly above, with forest ringing outward from the water's edge to the horizon. Come in autumn, and the larches by the lake turn gold first, gradually giving way to deeper green as the slope rises—as if the lake has been framed in gold. The water is clear as sapphire; when the wind passes, the pines sigh and the surface glints and shimmers.

What's most remarkable are its four mysteries: it never dries up in drought and never overflows in heavy rain, its water level constant for decades; it has no river flowing in or out, yet its water stays pure; the nearby lakes teem with fish, yet not a single fish lives here; and a sounding line dropped 300 meters still touches no bottom, with the lakebed hiding unknown fissures and underground rivers. These unsolved puzzles give Tianchi an ethereal sense of mystery.

Morning is best—mist drifts across the water, mountain shadows doze in the lake, and when the sun peeks out, the surface shatters into gold. Autumn is even more stunning: golden birches and dark green pines embrace the blue lake like an overturned palette— every shot is wallpaper-worthy.