In short
Sydney sits on a harbour, not on a grid. The CBD holds the offices and the Opera House; Surry Hills and Darlinghurst the restaurants and bars; Newtown and the Inner West the student life; Bondi and Coogee the south-eastern beaches; Manly the beach on the other side of the harbour.
The split matters: the eastern beaches and the north shore are separated by a water crossing, not by a street. Choosing a neighbourhood means choosing which half of the city will be far away.
Arriving and getting around
Ferries are public transport, not excursions. The Circular Quay–Manly route is part of the Opal network like any bus, and crosses the harbour in front of the Opera House and the bridge.
The Opal card — or a contactless bank card, accepted directly — caps daily and weekly spending, and Sunday has its own, lower cap. The airport train carries an additional station access fee specific to the airport, which does not count towards the cap.
The Blue Mountains are reached by suburban train to Katoomba, without a car.
What it really costs
Housing is the largest and tightest cost: Sydney is regularly ranked among Australia's most expensive cities on that measure.
"BYO" restaurants let you bring your own bottle for a corkage fee, which changes the budget of a dinner.
When to come
The southern summer (December–February) is hot, humid and crowded. October–November and March–April give the swimming without the crowds.
Vivid Sydney, in May–June, lights the city for three weeks in midwinter and fills the hotels. Mardi Gras, late February to early March, does the same.
What nobody tells you
The Bondi–Coogee coastal walk, six kilometres along the cliffs, passes five beaches and a clifftop cemetery. It is free and takes two hours: the best effort-to-view ratio in the city.
The red and yellow flags mark the patrolled zone. Swimming outside it is not a matter of comfort: rip currents are the leading cause of drowning on these coasts.
The rock pools (Bondi Icebergs, Bronte, Mahon) are filled by the tide and open to the public for a few dollars, or free depending on the site.