Legend has it that the spirits of Grandmother Suryakencana and Prabu Siliwangi kept Mount Gede Pangrango from erupting. Even now, at certain times, people flock to the caves around Gunung Gede to meditate or hold ritual ceremonies. According to local legend in Sukabumi, Situ Gunung is not a natural lake, it is a man-made lake. People say that the creator of the lake was Rangga Jagad Syhadana, a nobleman from the Mataram Kingdom.
In Sukabumi, the man who came from the Mataram Kingdom was known as Mbah Jalun. During the colonial period around the 1800s, Mbah Jalun fled from the Mataram Kingdom. After hiding in several Sultanates in Central Java, Mbah Jalun finally lived in the Sultanate of Banten. During his journey as a fugitive, Mbah Jalun stopped by the Kuningan area, West Java. Here Mbah Jalun married a woman from Kuningan. Together with his wife, Mbah Jalun then continued his journey to Cianjur. They passed Mount Gede Pangrango, until finally Mbah Jalun and his wife lived in a valley at the foot of Mount Pangrango in the Sukabumi area. In 1814, Mbah Jalun had a son named Rangga Jaka Lulunta.
Said to be a form of gratitude to God the Creator for their first son, Mbah Jalun made a lake. He finished making the lake using simple equipment in 7 days. He called the lake Situ Gunung, a lake located at the foot of the mountain. Since then until now, this lake is called Situ Gunung. The lake water comes from the waterfall Cimanaracun or Cimanaracun, located about 50 meters from the lake.
The local people of Sukabumi believe that the lake’s water discharge will never recede, even though the dry season arrives. They also believe that the lake water will decrease by itself when it is cleaned. Source: https://budaya-indonesia.org/Legenda-Situ-Gunung/