This is the easternmost edge of the Blue Mountains, where the plain on which
Sydney's western suburbs are built starts. That's Penrith in the middle distance.
The Nepean River is older than the mountains, which explains why it seems to
deviate into gorges in the mountains like this. There is a weir some kilometres
beyond where the river seems to disappear in this picture; that's how the river
level allows the "Nepean Belle" to navigate as far upstream as this.