Tianchi — Heaven Lake — is the volcanic crater lake at the summit of Changbaishan, sitting at 2,189 metres and ringed by bare rocky peaks that rise another few hundred metres above the waterline. The lake is large (9.8 square kilometres), deep (384 metres at maximum), and in favourable conditions a startling blue-green against the grey volcanic rock around it. It is among the most visually dramatic natural sites in northeast China, and the combination of altitude, remoteness, and geological improbability makes a strong impression on nearly everyone who reaches it.
The approach from the northern slope involves a shuttle bus to the base station and then either a steep walk up loose volcanic scree or a 4WD vehicle ride to the crater rim. The walk takes about thirty minutes uphill on a clear path but is genuinely steep. Weather at the summit is independent of conditions at the base — the lake disappears completely in cloud with little warning, and many visitors arrive at the rim to find nothing but white fog. The best weather windows are in late July and August, with September also reasonable but increasingly risky for cloud. Coming early in the morning improves the odds.
From the rim, on a clear day, you can see the lake spread across the caldera below and the North Korean peaks rising beyond it. The scale of what the original eruption created — a caldera nearly five kilometres across — becomes apparent only from this angle.