There is an overnight train from Cairns to Brisbane return,stopping at all the cities and towns along the Queensland coast, called the "Spirit of Queensland" which runs five days a week; you would leave the train at Tully which is a half hour drive to Sealords. If coming from Cairns, Tully it is a 3 hr trip, If coming from Townsville 4 hrs or Brisbane 21 hrs. There are three classes of travel; Rail Bed which is like air business class, premium economy and economy. The Cairns station is central with taxis available. Unfortunately the timing of the bus from Tully to Mission Beach does not align with train arrival times, however for a $30 charge Sugarland Car Rental Can pick you up if you are going to rent a car.
Cairns to Brisbane: Mon, Wed, Thu, Fri, Sun departing 9.00 am, arrive Tully 11.50 am
Brisbane to Cairns: Mon, Tues, Wed, Fri, Sat departing 3.45 pm, arrive Tully 1.00 pm the next day
Check the timetable at www.queenslandrailtravel.com.au/Planyourtrip/timetable