Night taxis slide away from Surabaya and the road becomes a black ribbon of rural lights as the van climbs toward Bondowoso; by midnight the engine hum is the only companion before the Ijen trek begins. At the ranger post you shoulder a headlamp and start a steady climb—an hour to 90 minutes of switchbacks and volcanic scree—until the crater rim opens and the electric-blue flames dare the night. The turquoise, 200‑meter‑deep lake smokes at the center while sulfur miners, packing sacks that can weigh 60–70 kg, move like silhouettes against the acid-steam.