This is the Taman Sari, or Water Palace next to the Yogya Kraton. It was also built starting in the 1750s as a sort of "pleasure palace" for the Sultan. Some of it was damaged by an earthquake in 1865.
Legend has it that the Sultan in those days had the Portuguese architect executed so nobody would find out the secret pleasure rooms inside the castle.
This is a carved stone gate to the water palace.
Go to the Kraton.
Go to Borobudur.