The Ijen volcano complex is a group of composite volcanoes located on the border between Banyuwangi Regency and Bondowoso Regency of East Java, Indonesia. It is known for its blue fire, acidic crater lake, and labour-intensive sulfur mining. It is inside an eponymous larger caldera Ijen, which is about 20 kilometres wide. The Gunung Merapi stratovolcano is the highest point of that complex.