Ijen: the blue fire at the bottom of an acid lake

Kawah Ijen is the most surreal landscape in Java. The crater holds a lake of turquoise water so acidic that it dissolves metal, ringed by yellow sulphur deposits and worked by miners who carry the rock out on their shoulders. At night, sulphur gas escaping from vents ignites into electric-blue flames, a phenomenon found in only a few places on earth.

The hike is short but steep, and the reward is not just the lake. The rim at dawn gives you the whole crater, the miners' path, the plume of gas and, on clear mornings, the mountains of the Ijen plateau and the sea beyond. It is a hard, strange, beautiful place, and it is increasingly popular, so go with realistic expectations and a proper mask.

The lake and the mine

The crater lake is about one kilometre wide and 200 metres deep, and its water has a pH of around 0.5, roughly comparable to battery acid. The turquoise colour comes from dissolved metals and sulphur, and the lake is the largest acidic lake in the world. It sits inside the Ijen volcano, which is part of a complex of older cones on the plateau.

Sulphur has been mined here for decades. Workers break the yellow crust from pipes and vents near the shore, fill baskets, and carry 70 to 90 kilograms up the steep crater path and then down to the weighing station. The loads are heavy, the gas is toxic, and the work is poorly paid. The mine is part of the landscape and the local economy, not a performance for visitors.

The blue fire

The blue flames are burning sulphur gas, not lava. Gas escapes from fissures at temperatures above 600 degrees Celsius and ignites on contact with oxygen, producing small, flickering blue flames that are most visible in complete darkness. The best time to see them is between two and four in the morning, when the crater is black and the gas is active.

Seeing the blue fire requires walking down into the crater in the dark, on a steep path of loose rock and sulphur, in a cloud of gas. It is genuinely hazardous. A good guide, a proper respirator and a calm assessment of the wind are essential. If the gas is blowing toward the path, do not go down. Many operators now discourage the descent, and you can see the glow from the rim on a good night.

The hike from Paltuding

The trail starts at Paltuding, a ranger post and car park at about 1,850 metres on the road from Banyuwangi. The path climbs three kilometres to the crater rim at 2,386 metres, gaining about 500 metres in altitude. Fit walkers do it in 90 minutes; most people take two hours, with stops. The path is wide and well used, but steep in places and dusty.

It is cold before dawn, often five to ten degrees, and the wind on the rim makes it colder. Bring a headlamp, a warm layer, gloves, water and a mask. The crater descent, if you do it, adds another 30 to 45 minutes each way and is much steeper than the main trail. Sunrise from the rim is around five thirty, and the light on the lake is the best part of the trip.

Getting there and where to stay

Banyuwangi is the gateway, a town on the strait between Java and Bali with an airport, a railway station and ferries to Bali from Ketapang. The drive to Paltuding takes about an hour and a half. Most visitors start around midnight from Banyuwangi or from the homestays nearer the park, reaching the trailhead at two or three in the morning.

Accommodation ranges from simple homestays in Licin and Tamansari to resorts on the lower slopes. The Ijen plateau is also coffee country, and a few plantations offer tours and stays. If you are coming from Bali, the ferry from Gilimanuk to Ketapang takes about 45 minutes, and the whole trip can be done in a long day, though a night is better.

Safety, fees and ethics

The gas is the main risk. Sulphur dioxide can cause coughing, breathing difficulties and, in high concentrations, serious injury. Anyone with asthma or respiratory problems should not descend into the crater, and nobody should go down without a respirator, not a cloth mask. Follow the guide, watch the wind, and turn back if the plume shifts.

The park charges an entrance fee and a separate fee for the crater descent in some periods. Guides are required for the descent and can be arranged at Paltuding or through your guesthouse. Do not encourage miners to pose for photographs in exchange for money; if you want to support them, buy a sulphur carving or use a local guide.

Practical and a plan

The dry season, April to October, gives the clearest nights and the best chance of seeing the blue fire and the lake. The wet season brings cloud, rain and slippery paths. The crater can be closed during periods of high volcanic activity, so check before you travel. Weekends are busy, and the trail can feel like a queue near the rim.

Most people visit Ijen between Bromo and Bali, which works well by road and ferry. Allow one night near the park, start at midnight, and plan to be back in Banyuwangi for a late breakfast.

• Day 1: drive from Bromo or Surabaya to Banyuwangi or the Ijen slopes.
• Night: depart at midnight, hike from Paltuding at 2 a.m., see the blue fire and the lake at dawn.
• Day 2: descend, visit a coffee plantation, then take the ferry to Bali or continue to Surabaya.
• Add a day for the Ijen plateau villages and the Jagir waterfall if you want a slower trip.

Questions people actually ask

Can I see the blue fire without a guide?

You can hike to the rim on your own, but the descent into the crater requires a guide and a respirator, and many operators will not take you down if the gas is strong. The blue flames are best seen from inside the crater, but the rim is safer.

How hard is the Ijen hike?

It is a steady three-kilometre climb with about 500 metres of ascent, which takes most people 1.5 to 2 hours. The path is good but steep. The crater descent is much harder and should only be attempted with a guide.

Is Ijen safe for people with asthma?

No. The sulphur dioxide can trigger severe respiratory problems, and the crater floor is not safe for anyone with asthma or a heart condition. Even on the rim, bring a proper mask and move away if the gas blows toward you.

Can I combine Ijen with Bali?

Yes. The ferry from Ketapang to Gilimanuk takes about 45 minutes, and Banyuwangi is connected by road to Bromo and Surabaya. Many travellers do Ijen at night and cross to Bali the same morning.