Did you know that you can climb Mount Ijen, an active sulfur volcano, located in East Java without having to hire a guide? Ijen volcano crater is a popular tourist destination in East Java due to the unique blue fire you can see inside the crater. All you need is the ability to drive a scooter and the confidence to be able to ask for directions to the locals.
FYI. You are not allowed down into the crater without a gas mask!