What is/are sculptures by the sea?
Sculptures by the Sea is basically an annual art exhibition show along Tamarama beach to Bondi beach, featuring a lot of installation works and sculptures. All you friend has to do is take a bus from Bondi Junction down to Tamarama beach then start walking until Bondi beach where they can grab lunch or swim at the beach. The exhibition is free btw !
Also some other places in Sydney I would recommend:
- Coastal walk: This is a 8.8km walk from Maroubra beach to Bondi beach. On the way, you pass beaches such as Coogee, Gordon's Bay, Clovelly, Bronte (my favourite beach!), Tamarama til you get to Bondi. You don't have to do the entire walk. You can start from Coogee to Bronte/Bondi. It usually takes around 2-4 hours, depending on your pace and stamina.
- Luna Park: It is an amusement park if your friend is interested in those
- Darling Harbour: You can visit Madame Tussauds, Sydney Aquarium and the Zoo. There are also bars and restaurants in the area if your friend prefers going during the night
- Taronga Zoo: very tourist-y spot
- Circular Quay as fantasticbeasts3 mentioned

would recommend the fish and chips they sell here!!
- Sydney Tower: Not only you get amazing views but you can also have a buffet with over 40 international dishes served. Though you do need to book in advance...
- Chinese Gardens: located in Darling Harbour. It's so cute and it's definitely a must go!
- Blue Mountains: If you friend has time, the mountains are a 2-3 hour train ride away from Central if I'm not mistaken
- Art Galleries: Would recommend the Art Gallery of New South Wales and Museum of Contemporary Art. Works from the Rijksmuseum in the Netherlands (made by Rembrandht and other) will be displayed from tomorrow til Feb.
- The Rocks: A lot of history here!
- St Mary's Cathedral: This is a very tourist-y spot. Nice place to take photos.
- Royal Botanical Gardens: just a nice nature, outdoor-sy area to go to.
- Newtown: probably the MOST hipster place I have ever visited. They have good restaurants and bars here. Just a 10-15 minute bus ride from Central.
- Manly beach: Haven't visited but I've heard its a really nice beach
- Watson's Bay + Camp Cove: Watson's bay is just a 20-30 minute bus ride from Bondi Junction or you can catch a ferry from Circular Quay. The Camp Cove beach is a five minute walk from Watson's Bay but its a really small beach. It's quite nice as it isn't as busy as Bondi or Coogee.
I feel like there's more but that's all basically from the top of my head ^^