Krakatoa, or Krakatau (Indonesian: Krakatau), is a volcanic island situated in the Sunda Strait between the islands of Java and Sumatra in Indonesia. The name is also used for the surrounding island group comprising the remnants of a much larger island of three volcanic peaks which was obliterated in a cataclysmic 1883 eruption, unleashing huge tsunamis (killing more than 36,000 people) and destroying over two-thirds of the island. The explosion is considered to be the loudest sound ever heard in modern history, with reports of it being heard up to 3,000 miles (4,800 km) from its point of origin. The shock waves from the explosion were recorded on barographs around the globe.
In 1927 a new island, Anak Krakatau, or "Child of Krakatoa", emerged from the caldera formed in 1883 and is the current location of eruptive activity.

Mount Gede or Gunung Gede (Big Mountain in Sundanese) is a stratovolcano in West Java, Indonesia. The volcano contains two peaks with Mount Gede as one peak and Mount Pangrango for the other one. Three major cities, Cianjur, Sukabumi and Bogor, are located in the volcano complex at the east, south and northwest, respectively, along with suburban growth. Seven craters are located in the complex: Baru, Gumuruh (2,927 m), Lanang (2,800 m), Kawah Leutik, Ratu (2,800 m), Sela (2,709 m) and Wadon (2,600 m). Historical volcanic activity has been recorded since the 16th century. With the amalgamation and growth of Greater Jakarta with those 3 cities, dense suburban growth has engulfed the fringes of the volcano, home to roughly 4 million people.

Mount Salak (Indonesian: Gunung Salak, Sundanese: Gunung Salak) is an eroded volcanic range in West Java, Indonesia. Several satellite cones occur on the southeast flank and on the northern foot. Two craters are found at the summit. Mount Salak has been the site of a geothermal exploration.
According to popular belief, the name "Salak" comes from salak, a tropical fruit with scaly skin. However, according to Sundanese tradition, the name was derived from the Sanskrit word "Salaka" which means "silver"; thus, Mount Salak means "silver mountain".

Tangkuban Perahu (spelt Tangkuban Parahu in the local Sundanese dialect) is a dormant volcano 30 km north of the city of Bandung, the provincial capital of West Java, Indonesia. It last erupted in 1826, 1829, 1842, 1846, 1896, 1910, 1926, 1929, 1952, 1957, 1961, 1965, 1967, 1969, 1983. It is a popular tourist attraction where tourists can hike or ride to the edge of the crater to view the hot water springs and boiling mud up close, and buy eggs cooked on the hot surface. This stratovolcano is on the island of Java and last erupted in 1983. Together with Mount Burangrang and Bukit Tunggul, those are remnants of the ancient Mount Sunda after the plinian eruption caused the Caldera to collapse.
In April 2005 the Directorate of Volcanology and Geological Hazard Mitigation raised an alert, forbidding visitors from going up the volcano. "Sensors on the slopes of the two mountains - Anak Krakatoa on the southern tip of Sumatra Island and Tangkuban Perahu in Java - picked up an increase in volcanic activity and a buildup of gases, said government volcanologist Syamsul Rizal."

Mount Papandayan is a complex stratovolcano, located in Garut Regency, to the southeast of the city of Bandung in West Java, Indonesia. It is about 15 km to the southwest of the town of Garut. At the summit, there are four large craters which contain active fumarole fields. An eruption in 1772 caused the northeast flank to collapse producing a catastrophic debris avalanche that destroyed 40 villages and killed nearly 3,000 people. The eruption truncated the volcano into a broad shape with two peaks and a flat area 1.1 km wide with Alun-Alun crater in the middle, making the mountain look like a twin volcano. One of the peaks is called Papandayan and the other Mount Puntang.
Since 1772, only small phreatic eruptions were recorded before an explosive eruption that began in November 2002. More recently, the volcano has been quite active. On August 14, 2011 the volcano's warning status was lifted from Level II, "Vigilant" (Indonesian: Waspada) to Level III, "Alert" (Siaga) following the emission of dangerous hydrogen sulfide and carbon monoxide gases. People, including tourists, were urged to remain at least 2 kilometers (1.2 mi) from the yellow craters on the 2,665-meter (8,743-foot) Mount Papandayan. On Friday September 2, 2011, the Indonesian Volcanology and Geophysical Disaster Mitigation Center reported that numerous shallow volcanic earthquakes had been recorded along with other indications of volcanic activity. A spokesperson for the Indonesian National Disaster Management Agency noted that if Mt Papandayan erupted, over 170,000 people living in five nearby subdistricts (kecamatan) and in twenty villages could be affected. Of the people likely to be affected, it was expected that perhaps as many as 11,500 people might need to be evacuated.

Mount Merapi, Gunung Merapi (literally Fire Mountain in Indonesian/Javanese), is an active stratovolcano located on the border between Central Java and Yogyakarta, Indonesia. It is the most active volcano in Indonesia and has erupted regularly since 1548. It is located approximately 28 kilometres (17 mi) north of the large Yogyakarta city, and thousands of people live on the flanks of the volcano, with villages as high as 1,700 metres (5,600 ft) above sea level.
Smoke can be seen emerging from the mountaintop at least 300 days a year and several eruptions have caused fatalities. Pyroclastic flow from a large explosion killed 27 people on 22 November in 1994, mostly in the town of Muntilan, west of the volcano. Another large eruption occurred in 2006, shortly before the Yogyakarta earthquake. In light of the hazards that Merapi poses to populated areas, it has been designated as one of the Decade Volcanoes.
On 25 October 2010 the Indonesian government raised the alert for Mount Merapi to its highest level and warned villagers in threatened areas to move to safer ground. People living within a 20 km (12 mi) zone were told to evacuate. Officials said about 500 volcanic earthquakes had been recorded on the mountain over the weekend of 23–24 October, and that the magma had risen to about 1 kilometre (3,300 ft) below the surface due to the seismic activity. On the afternoon of 25 October 2010 Mount Merapi erupted lava from its southern and southeastern slopes.
The mountain was still erupting on 30 November 2010 however due to lowered eruptive activity on 3 December 2010 the official alert status was reduced to level 3. The volcano is now 2930 metres high, 38 metres lower than before the 2010 eruptions.
After big eruption in 2010 the characteristic of the Mount Merapi is changed. On November 18, 2013 Mount Merapi bursted smoke up to 2,000 meters height, one of its first major phreatic eruption after the 2010 eruption. Researchers said that this eruption occurred due to combined effect of hot volcaninc gases and abundant rainfall.

Semeru, or Mount Semeru (Indonesian: Gunung Semeru), is an active volcano located in East Java, Indonesia. It is the highest mountain on the island of Java. The stratovolcano is also known as Mahameru, meaning 'The Great Mountain. The name derived from the Hindu-Buddhist mythical mountain of Meru or Sumeru, the abode of gods.
Known also as Mahameru the (Great Mountain), it is very steep rising abruptly above the coastal plains of eastern Java. Maars containing crater lakes have formed along a line through the summit of the volcano. It was formed south of the overlapping Ajek-ajek and Jambagan calderas. Semeru lies at the south end of the Tengger Volcanic Complex.
Semeru's eruptive history is extensive. Since 1818, at least 55 eruptions have been recorded (10 of which resulted in fatalities) consisting of both lava flows and pyroclastic flows. All historical eruptions have had a VEI of 2 or 3.
Semeru has been in a state of near-constant eruption from 1967 to the present. At times, small eruptions happen every 20 minutes or so.
Semeru is regularly climbed by tourists, usually starting from the village of Ranu Pane to the north, but though non-technical it can be dangerous. Soe Hok Gie, an Indonesian political activist of the 1960s died in 1969 from inhaling poisonous gases while hiking on Mount Semeru.

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 meters (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park. The name of Bromo derived from Javanese pronunciation of Brahma, the Hindu creator god.
Mount Bromo sits in the middle of a vast plain called the "Sea of Sand" (Javanese: Segara Wedi or Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 m or 9,088 ft) (Indonesian: Gunung Penanjakan). The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.
Depending on the degree of volcanic activity, the Indonesian Centre for Vulcanology and Disaster Hazard Mitigation sometimes issues warnings against visiting Mount Bromo.