This is Sydney Observatory built on a hill overlooking Sydney harbour right above the Opera House and next to the bridge. It was built on land that was called Miller's Point because there was a big windmill there to grind the grain for the new settlement. They started building a fort and a signal station there too but all that was torn down before this structure was built from sandstone in 1859.
The Observatory was important to give the correct time to the ships in the harbour, for weather observation as well as astronomical observation. There are two copper telescope domes, one holds a 29 cm refractor telescope dated from 1874. The northern dome now has a modern telescope for pubic observing.
Originally the Goverment astronomer and his family lived in the building and the structure to the right of the central tower was their accommodation.
This historic building is now part of the Powerhouse museum and is open to the public.
This is a lovely building but I wish that big windmill from 1804 was still there too.