When you think of lava, you probably imagine glowing red and orange liquid flowing over a rocky plain. And in most places, you'd be exactly right. Lava is typically orange and red.
But not always.
Photographer Reuben Wu learned this firsthand on a trip to Indonesia's Ijen volcano, where he saw the aptly named Blue Fire Crater, which is famous for its molten sulfur lava that burns a brilliant sapphire blue.
The trek to see this blue lava is not an easy one.
It's a two-hour hike up the mountain, and then another 45 minutes down into the crater itself. Inside the crater, sulfur cooks at temperatures exceeding 1,000 degrees Fahrenheit.
But it's worth it to see this incredible natural phenomenon.
There are other places on Earth that produce blue lava like this, but Ijen's crater is the largest. For that reason, it's a popular tourist destination, despite the climb.
To really capture the otherworldly magic of this place, Wu stayed until after dark, using only the light of the moon and of the lava itself to take his photos.
It doesn't look real, but it is.
The molten sulfur is not only hot, but can also shoot sixteen feet into the air.
Bromo, Batuk, and Semeru mountains.
Wu also explored these mountains, which are a few hours away from Ijen.