Bromo Tengger Semeru National Park is a national park located in East Java, Indonesia, to the east of Malang and Lumajang, to the south of Pasuruan and Probolinggo, and to the southeast of Surabaya, the capital of East Java. It is the only conservation area in Indonesia that has a sand sea, the Tengger Sand Sea, across which is the caldera of an ancient volcano (Tengger) from which four new volcanic cones have emerged. This unique feature covers a total area of 5,250 hectares at an altitude of about 2,100 meters (6,900 ft). The massif also contains the highest mountain in Java, Mount Semeru, four lakes and 50 rivers. It is named after the Tengger tribe. The explosion of the volcano that created the caldera, happened ca. 45.000 years ago, in an event similar to the Krakatau eruption.

East Java is a province of Indonesia located in the easternmost third of Java island. It has a land border only with the province of Central Java to the west; the Java Sea and the Indian Ocean border its northern and southern coasts, respectively, while the narrow Bali Strait to the east separates Java from Bali by around 2.29 kilometres (1.42 mi). Located in eastern Java, the province also includes the island of Madura, as well as the Kangean islands and other smaller island groups located further east and Masalembu archipelagos in the north. Its capital is Surabaya, the second largest city in Indonesia, a major industrial center and also a major business center. Banyuwangi is the largest regency in East Java and the largest on the island of Java.