Sydney is honestly one of the safer major cities for solo women. I felt completely comfortable walking alone during the day everywhere from The Rocks to Bondi Junction and at night in well-lit areas around Circular Quay, Martin Place, and Darling Harbour precincts.

Avoid walking alone late at night around Central Station's Eddy Avenue/Elizabeth Street areas after 10pm, and stick to main thoroughfares in Redfern or Surry Hills after dark. Kings Cross has cleaned up massively but still use normal city sense around Darlinghurst Road late night.

Standard city precautions apply around Town Hall station concourse and Hyde Park after 11pm - don't flash expensive items, trust your instincts, stay on well-lit George Street or Pitt Street corridors. But overall much safer than most cities I've visited solo, and police presence is visible around Circular Quay and The Rocks.