I set off to walk from Manly beach to Spit bridge. That would be, I found out later, a 10km walk. In the end, I got distracted by Northhead, a promontory in between Manly beach and the bridge, which adds a few km of walking and a few hundred metres of elevation. Once up there, you can explore the barracks and old military emplacements, and get some great views out over Sydney.
Once I’d walked back down – via a lovely sandy bike track, then a steep road – I was back to crowds of people enjoying the sun and mobbing Manly itself. Relative peace was easy to find by following signs to the Spit bridge walk, though, with quieter beaches and shaded spots around the corner.