Being based in Sydney gives you the opportunity to jump on the train at Sydney Central and head across to the Blue Mountains – but definitely set off early so you can make the most of it in the day. (Not much point staying overnight, in all honestly.)
The Blue Mountains are both a National Park and a UNESCO World Heritage Area. Lots of Sydneysiders head there on the weekends, so if you’re a tourist its best to visit on a weekday as it’ll be a lot quieter. And it doesn’t have to be an expensive day trip if you plan it well. No need to hire a car or pay for taxis when you can take buses and walk.