A 200 km (125 mile) trek down the coast from Sydney (marginally closer than the inland Canberra) is the small tourist port of Jervis Bay. The area is known for its preserved wetlands and marine activities, where you can catch sight of rare birds on a path through Jervis Bay Nature Reserve or utilize in-town tour operators to whale and dolphin watch. Don't stop at basic tourist behavior, though. You may traverse the bay via anything from kayak to cruise-liner (although only one these you'll be in full control of), or enjoy some of the best scuba diving in New South Wales. That's right, if diving is your style then be prepared to view everything from nurse sharks to sea dragons and fur seals at a number of locations in the bay. Then again, you could just stroll along the waterfront until you find a comfortable spot and let the day mosey by.
The included tourism site is quite helpful in coordinating particular activities you may be looking to include in your itinerary. Otherwise, you can just take a ride into town and soak in small town coastal Australia on the fly.