The Water Palace, built in the 1750s by Hamengkubuwono I, was a royal leisure complex of bathing pools, islands, and underground passages connected by canal. The sultans used it as a retreat and pleasure garden. Today, much of the compound is in attractive ruin, with some pools restored and parts of the old network of tunnels accessible to visitors.
The most photogenic section is the Umbul Binangun bathing complex — three pools surrounded by high walls and a two-story viewing pavilion. Arrive early to have it to yourself; by 9am tour groups fill the place. Beyond the main pool, the kampung that grew inside the old palace walls is worth exploring on foot: a dense labyrinth of lanes, batik sellers, and painted houses built directly into the old masonry. Artists have colonised the upper section of the ruins and several open studios. The adjacent Sumur Gumuling underground mosque — connected by tunnel — is usually visited as part of the same circuit.