I'm sure everyone has heard of the famous Harbour Bridge Climb however this can be expensive and maybe not for people who aren't really into extreme activities or heights.
Walking across the Harbour Bridge is a great way to get almost the same view and enjoy walking right across the iconic Harbour Bridge for free! Depending on how quickly you walk or if you have children with you etc it can only take around 30-45mins to walk from one end to the other and is a really enjoyable free activity to pass the time on a sunny day.
You can enter the bridge from either end, either starting at Milson's Point and walking across from that side leading you towards the city and you leave the bridge via the rocks. Or you can enter from the Stairs opposite the Glenmore Hotel in the rocks and walk across the bridge ending up at Milson's Point in North Sydney. The entrance to the bridge at Milson's Point is right by the train station so if you're coming from the city you can either get a train to Milson's Point and then walk back over the bridge or if you start from the city side and walk over to Milson's Point you can always have the option of getting a train back if you don't feel like walking both ways.
There are high metal barriers along the walkway however you can still see over the top of them views of the Opera House and all across the harbour as you're walking. Plus you walk right through the 2 big stone pillars and get some really cool views of the bridge itself as you're walking.
One thing to note is if you do have children with you and have a stroller... both ends of the bridge getting on and off the walkway has a lot of steps, so you will need a hand to carry the stroller up/down the steps to access the walk. This activity is a really good idea if you're on a budget as its completely free and a great way to pass the time if you're visiting Sydney or want something touristy to do that doesn't break the bank.