As they make their way down narrow, water-filled crevices, canyoners need to combine the skills of swimming and bushwalking with those of rock climbing and abseiling. With more than 300 deep, narrow clefts in its high sandstone plateau, some of which are up to 330 feet deep but only a few metres wide, the Blue Mountains offer the best canyoning in the country. Several Katoomba companies offer guided trips and tuition.