Lumajang in the context of Bromo Tengger Semeru National Park

Bromo Tengger Semeru National Park (Indonesian: Taman Nasional Bromo Tengger Semeru; abbreviated as TNBTS) is a national park located in East Java, Indonesia, to the east of Malang, to the west of 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 (Indonesian: Laut Pasir Tengger), 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 (3,676 meters (12,060 ft)), four lakes (including, the isolated Ranu Tompe), and 50 rivers. It is named after the Tenggerese people. The explosion of the volcano that created the caldera, happened ca. 45.000 years ago, in an event similar to the Krakatau eruption.

The Tengger Sand Sea has been protected since 1919. The Bromo Tengger Semeru National Park was declared a national park in 1982.

Madurese (/ˌmædʒʊˈriːz/ MAD-juh-REEZ; Bhâsa Madhurâ, Pegon script: ݒا࣪سا ماڊۅرا࣪, Carakan script: ꦧꦱꦩꦝꦸꦫ, IPA: [bʰɤsa maʈʰurɤ]) is a language of the Madurese people, native to the Madura Island and eastern part of Java, Indonesia; it is also spoken by migrants to other parts of Indonesia, namely the Surabaya, Malang, Gresik, eastern salient of Java (comprising Pasuruan, Bondowoso, Probolinggo, Situbondo, Jember, Lumajang, to Banyuwangi), the Masalembu Islands, Raas Islands, and some on Kalimantan. It was traditionally written in the Javanese script, but the Latin script and the Pegon script (based on Arabic script) is now more commonly used. The number of speakers, though shrinking, is estimated to be 10–14 million, making it one of the most widely spoken languages in the country. Bawean language, which is a dialect of Madurese, is also spoken by Bawean people in Bawean Island, Indonesia. Then also by their descendants in Malaysia and Singapore.

The Regreg War (often erroneously called the Paregreg) was a civil war that took place in 1404–1406 within the Javanese empire of Majapahit. The conflict was fought as a war of independence between the Kedhaton Kulon (Western court) led by Wikramawardhana against the breakaway Kedhaton Wetan (Eastern court) of Blambangan led by Bhre Wirabhumi. This war of rivalry and secession had caused calamity, crisis, court's preoccupation, the drain of financial resources, and exhaustion, which is thought to be one of the causes of Majapahit's decline in the following years.