Queen's Park slopes down hill towards the west from its Bondi end so is the perfect place to catch a Sydney sunset. There are plenty of seats throughout the park or a great place to sit is on the 'cliffs' at the Bondi end to get some added height. Take some snacks, some wine (if you so desire) and a picnic blanket for after the sun sets. With the right amount of cloud cover, it makes for a truly magical sight.
As the sun sets, the bats migrate overhead, some landing in the nearby trees. It's a try Sydney experience.
Queen's Park has the added bonus of being dog friendly so you can take your pooch with (and if you don't have one you can watch all the doggies play).