They are called mountains but they'remore like canyons and gorges, from the bottom of which the top does seem quite high! It's called the Blue Mountains since the pines make a kind of blue-ish haze, very dense jungle type areas and lots of really beautiful waterfalls.
We went to an area called Wentworth falls and walked along the Wentworth pass to Empress falls. The first part of the walk is quite touristy by the falls, then you start to go down some extremely steep stairs and ladders to get to the bottom of the canyon. They're the reason for the 'hard' grading in the walk book I think, the rest of the walk is not too bad and only about 6k. It takes about 3 hours though with all the ladders and having a paddle in the pools and the bottom of the falls!
A map of where we went is here, but bewarned the stairs are quite tough!
