Bondi Beach is probably Sydney's most well known beach, and it features many popular cafes, restaurant and hotels with great views of the shore, which is about one kilometer long.
A great scenic walk is to do a small hike from Bondi Beach to Coogee Beach. In addition to great excersise the walk, which takes about an hour overlooks several of Sydney's beaches.
If you are interested in an overnight or long day trip, you should also visit the Blue Mountains, one of Australia's premier national parks.
The Blue Mountains are known for hiking and abseiling, both which are best to do in the morning when it is not as hot out.