What is Ijen Crater?! Literally it is a carter in the active volcano and located in east Java Indonesia. The extraordinary thing about Ijen Crater is the blue fire.
You may wonder, how could it be? Fire supposed to be red right?! For your information, under the volcano, there are continuous streams of sulfur and it blasts out from vent. The blasts are also toxically high level of sulfur gas, that is why it requires a gas mask when around the caldera. The blast of sulfur gas is yellow color, when it hits oxygen and combained the air temperature around 360°C and then boom! the fire turns blue.
Another wonderful thing about Ijen Crater is the blue (turquoise) massive, largest and most acidic lake in the whole world, besides the blue fire and blue lava. It is extremely dangerous and forbidden to get close with the lake.
Kawah Ijen (in bahasa) is one of the few place left on Earth that naturally produce sulfur mineral in large amount of deposit. This condition makes mine the sulfur becomes a primary source of work. Unfortunately the miners have to mine heavily and with low pay (only IDR 1K/kg of sulfur!!!), though they have to face highly toxic gas and dangerous trek risks.
The miner should trek up for about 4 km and the first 2.5 km the angle of the land ia around 45°. After trek up they have to face the down trek, for about 500 meters down to the caldera, for your information, they do not use a safe gas mask, they just tied clothes around their nose and mouth (even the gas makes your eyes watering).
They mine twice a day and once they mine, they bring 70-100 kg sulfur mineral (yellow color) with kind of two bamboo baskets with a 1.5 meters long wood/bamboo to hang on the baskets on a single shoulder.
The best moment to enjoy the view in Ijen Crater is when the sunrise, so the trek should be started at 2 AM. The other suggestion is never wear your favorite clothes because it will be smelled acidic for long time despite washing it.
Prepare your body condition, listen up to your trekking guide, use a safe gas mask that covered your eyes, nose and mouth. Grab every single beautiful view of Ijen Crater, cheers!