Let’s just admit that Sydney offers a lot and 24 hours in Sydney is a very less time to explore the beautiful city. However, if I have just 24 hours in Sydney, then:
I would definitely start my tour in Sydney, by taking a ferry to Taronga Zoo. It is definitely a must do. Taronga Zoo has a huge variety of animals and the encounters with the animals are definitely worth the visit. According to Wikipedia, Taronga Zoo has about 340 species and over 2,600 individual animals.
I would take the ferry back to Circular Quay. Circular Quay is a harbour in Sydney. The views of the famous Sydney Opera House on the right and the Sydney Harbour Bridge on the left are something to die for – especially on a warm sunny day.
A short walk from Circular Quay leads to The Rocks. The Rocks features many restaurants and craft shops. The Rocks Market operate on every weekend, with around 100 shops.
After The Rocks, I would head to Darling Harbour and witness the vibrant and colourful part of Sydney. Most often Darling Harbour has some festival celebration or the other. If not, not to worry, as Darling Harbour has some amazing pubs and bars.