This lovely section of Ku-ring-gai Chase National Park has two entrance points joined by a road that snakes through glorious bushland down to Cowan Creek, a tributary of the Hawkesbury River. Its fame as a beauty spot has made it prime weekend picnic territory since the 1930s, but midweek you'll have it to yourself. Excellent bush tracks run from both entrances down to Bobbin Head itself, where there's an information office, boat hire and a couple of eateries.
Three kilometres from Bobbin Head, on the road up to Mt Colah, the Kalkari Discovery Centre has a small exhibition and a short loop track that has some great information about local tree species and also gives you the chance to see eastern grey kangaroos and other wildlife.
At Bobbin Head, pedal boats are available from the Bobbin Inn by the information centre. For boats, 'tinnies' seating six can be hired at the marina (02-9457 9011; $80 for two hours, $160 for a day) and include a fishing license. The marina's cafe is a nice spot to sit by the water eating some fish.
Buses from Turramurra station will drop you at the end of Bobbin Head Rd, where you have a choice of two tracks to reach the bottom (3.5km and 6.5km), one beginning at a curious sandstone sphinx carved by a war-wounded soldier as a WWI memorial. From the Mt Colah entrance, follow the Kalkari and Birrawanna tracks (6km). Another trail leads in from near Mt Ku-Ring-Gai station (5.5km). You can also get here on a river cruise from Palm Beach.