Complex sentence: Gede Pangrango volcano in West Java also a popular hiking destination, especially among domestic hikers, while Mount Tambora in Sumbawa with its historical massive volcanic eruption back in 1815 that produced massive caldera also had gained attention among hikers.
Split into simpler sentences: Gede Pangrango volcano in West Java also a popular hiking destination, especially among domestic hikers. In Sumbawa, Mount Tambora with its historical massive volcanic eruption back in 1815 that produced massive caldera also had gained attention among hikers.