It’s a canal chicane, built by our previous Sultan (Yap, City of Yogyakarta, Indonesia is still have a sultan palace - He was Sri Sultan Hamengkubuwono IX) in mid 20th century. He decided to build the canal to prevent his people being exiled by the Dutch colonial to other countries to be forced to work as a slave, by using them as the workers. Today, the canal also has a function as an irrigation, make its surround fertile.