The Jantar Mantar observatory , constructed in 1737 , is located above the ghats along the Ganges , and is adjacent to the Manmandir and Dasaswamedh Ghats and near the palace of Raja Jai Singh of Jaipur . While less equipped than the observatories at Jaipur and Delhi , the Jantar Mantar have a unique equatorial sundial which is functional and allow measurements to be monitored and recorded by one person .