Kawah Ijen acid lake

Kawah Ijen is a volcanic crater in East Java, Indonesia, containing a strikingly coloured acid lake and active sulfur vents. It is internationally known for the turquoise acidic lake, the sulfur mining that continues on its inner slopes and the nightly ‘blue fire’ seen where sulfur gases ignite.

A dramatic crater with a highly acidic, mineral-rich lake at its centre, accessible by hiking routes that lead to rim viewpoints and the mining areas. Many visitors join guided pre-dawn treks to descend near the vents to observe the blue flames and then watch sunrise from the crater rim; sulfur miners working the site remain a prominent human presence.

The Ijen complex has long been exploited for sulfur extraction; miners remove solidified sulfur from fumaroles and transport loads down the crater. The site has attracted scientific and tourist interest because of its unusual volcanic gas phenomena and the working landscape.

Kawah Ijen sits within the Ijen volcanic complex in eastern Java, Indonesia, inside a rugged volcanic highland area that is typically accessed from regional towns in Banyuwangi and Bondowoso.

• Acidic lake safety: The lake is highly acidic and stained turquoise by dissolved minerals; swimming is unsafe and water is unsuitable for consumption.
• Blue fire and sunrise treks: Night and pre-dawn treks are organized to view the ‘blue fire’ phenomenon when burning sulfur gases are visible, often combined with sunrise views over the crater.

What to See#

• Kawah Ijen crater lake: The acid crater lake at the centre of the Ijen volcanic complex noted for its vivid turquoise colour caused by high sulfuric acidity and dissolved minerals.
• Blue fire (sulfur combustion) site: The blue flame site where sulfur gases ignite and produce an intense blue fire visible before dawn; a common destination for guided night treks.
• Sulfur mining areas: Active sulfur mining workings on the inner crater slopes where miners extract and transport solidified sulfur from vents to weigh stations outside the crater.

Kawah Ijen is reached by driving to the Paltuding (Pos Paltuding) trailhead on the Ijen caldera rim, which is accessed by mountain roads from Banyuwangi (east) or Bondowoso (northwest). From the Paltuding parking area visitors hike up to the crater rim and then, if visiting the acidic lake, descend to the crater floor on the marked trail; the trail is steep and hikers commonly start very early (or at night) for the sunrise/blue‑fire visits.

• Start the trek from the common Paltuding trailhead before dawn if you want to see the famous blue fire and catch sunrise from the crater rim; blue flames are only visible in pre-dawn darkness.
• Avoid visiting in the heat of the day when sulfur fumes tend to be stronger - aim to be on the rim at first light and off the crater floor as the sun climbs.
• Arrange a local, licensed guide and confirm they provide or advise on certified gas masks before you descend; many visitors underestimate how quickly fumes can affect visibility and breathing.
• Reduce travel stress by staying overnight in Banyuwangi (the closest town with regular transport and guides) so you can start the hike very early without a long pre-dawn drive.