There is so much to see and do in Sydney at night. First stop, Darling Harbour. Darling Park is just fantastic - it was recently transformed into a children's playground and family picnic area; and yes, even in the twilight hours (and in cold weather as well) you will see children on the swings, people watching street theatre or watching sporting events in tandem with other events that happen quite frequently at Darling Harbour. There is always an abundance of signage around Darling Harbour telling you what is on for any given calendar month - for example firework displays and salsa dancing and other artistic performances. There is also a free salsa dancing night every week at the Hard Rock Cafe.
Darling Harbour is also a great destination to enjoy a few cocktails (well, Sydney is the cocktail city after all) and a cheap feed, at establishments such as Blackbird Cafe, where you can enjoy the stunning backdrop of Sydney Harbour, views of the marina, The Star Casino and Harbourside. Excellent outdoor heating makes it possible to sit outside at this establishment at night Thai Foon is another great restaurant to eat out at night, where stunning views of Darling Harbour and the city skyline can also be enjoyed.
Darling Harbour is also the best location in Sydney to go ten-pin bowling. Strike bowling at King Street Wharf is just great once in a while, and sometimes they run their tight-arse Tuesday nights. Otherwise Kingpin bowling at Harbourside would be my second preference when it comes to ten-pin bowling at Darling Harbour; again, the perfect location if you are in the mood to go ten-pin bowling with either one other person, or with a group of people.
These establishments are super busy on a Saturday night. Otherwise for something a bit more adventurous, opt in on a twilight sailing experience, and who knows you might end up driving the yacht along Sydney Harbour. Boating underneath the Sydney Harbour Bridge is just stunning at night. Otherwise, a ferry ride on any of the Sydney ferries is just beautiful at night. Otherwise, if the recently opened Madame Tussauds takes your fancy, then go for it.
Circular Quay and Hyde Park are also great Sydney landmarks to visit at night. It is just bliss walking through Hyde Park on a Thursday night in particular (after late night shopping, or spending a bit of time at Pitt Street Mall) where you walk towards and then past St James train station (you start at the waterfall and you turn right towards Oxford Street) you might be lucky to see some art when that is on, or otherwise come in October, when the (as part of the Crave International Food Festival) night noodle market provides great ambience, and comfortable food to enjoy and chill out at Hyde Park. You will feel like you are in Europe when you are walking through Hyde Park with the stunning lights reflecting on the well maintained trees.
The Art Gallery of New South Wales is a great call if you love art, especially with their 'Art After Hours' series which usually falls on a Wednesday night. An appreciation night for the arts, that's for sure. Perhaps you might be inspired to do a bit of study, then the refurbished State Library of New South Wales provides an awesome and inspiring working space.
It is great to see a film at Dendy at Opera Quays, and then immediately afterwards you are heading outside and spending a bit of time walking slowly towards the Sydney Opera House with stunning views of the Sydney Harbour Bridge. Great to admire and stare at, before heading back towards where the ferries depart, and towards Circular Quay train station.
Many of Sydney's best and most popular free events provide a great reason for many Sydneysiders to ditch the couch at home for a night (at least) and come out and enjoy this beautiful harbour city. Think annual events such as Vivid Sydney. See, plenty to do to get you started on enjoying a great night out in Sydney.