The Riverboat Postman is the famous Hawkesbury Mail Boat that delivers the mail and other essentials to the river-access-only settlements upriver from Brooklyn. It leaves the wharf at 10am each weekday except public holidays, regardless of the weather as it delivers mail on behalf of the Australia Post.
Its has friendly staff, great coffee and lunch ( included in ticket price) with nice views of Hawkesbury River around Brooklyn. Its the perfect day out relaxing on a three hour cruise for families. They are located right next to the Hawkesbury River Train Station at Brooklyn.

Check their website for ticket prices and bookings as online booking is essential before going.
https://riverboatpostman.com.au/prices