The grand canyon is one of the most beautiful walks in the blue mountains.  Rated hard, it is 3-4 hours walk from the grand canyon loop car park.  It took us 4 hours including many stops to enjoy and for lunch.  We walked it according to the NPWS walking guide.  This is the same way as recommended in Wild Walks. Many people we passed were doing it the other way, starting at the lookout.  I think this is harder as the climb back out takes you back out at Neates Glen which is higher than the lookout.