Fitzroy Island is a great day trip from Cairns. It's only a ferry ride away, has heaps of activities (snorkeling, bushwalking, glass bottom boat tours, kayaking tours and more) and won't break the budget.
I visited Fitzroy on a pretty dreary, rainy day however, which left me disappointed that I wouldn't be able to see as much of the beautiful surrounds as I would have liked. But then I decided to go on a tour of Fitzroy Island's Turtle Rehabilitation Centre, which offers an
amazing, unique experience in any weather.
The Fitzroy Island Turtle Rehabilitation Centre is only a few years old and is an extension of the
Cairns Turtle Rehabilitation Centre. It was built after 2011 Cyclone Yasi prompted a huge spike in the number of sea turtles needing help and the Cairns centre proved too small to handle them all (Yasi ripped up much of the area's sea grass, causing turtles to starve). A lot of fundraising had to be done to get the centre going, which took years, but in 2013 the Fitzroy Island centre opened (you can read about the process
here).
Since the centre still survives on donations, it's a pretty modest place, and the tour mostly involves standing round a tank out the front as you
watch the strongest turtle in residence get fed and listen to a talk (generally, the turtles get assessed and receive emergency care in Cairns, then come out to Fitzroy to regain their strength before being released).
This talk is by no means disappointing though; you get to hear stories about the turtles currently on Fitzroy, including what kind they are and why they're here (turtles might have been hit by a boat, swallowed plastic, are malnourished, or have something else wrong with them).
My favourite part of the tour was hearing about all the times the turtles have gotten angry with the volunteers who look after them. Turtles have great facial recognition, so if someone does something they don't like, such as move them between tanks, or not allow them to play with an important piece of equipment, that person might get splashed with water or be ignored for months.

Feeding time

The turtle popped up right in front of me
The rehab centre tours start outside the Fitzroy Island Resort (which pays for the centre's land lease) and you're apparently supposed to book at the hotel's reception, however I was sent to nearby shop, so don't be surprised if that happens. The cost of the tour is around $8 (I was told it was $8.80, but am equally sure I received too much change for that to be what I was actually charged). Most marketing material says tours run once a day, at 2pm, but I went on one at 1pm, which was one of two being held on that day (in January).
I highly recommend the tour, but with so much to do on this island, and some of the other tours potentially running at clashing times (since they depend on the weather), it may well not fit into your day. In that case, you can still learn a lot about the centre's work if you
walk past it on your way to the lighthouse and read the information panels out front. You might even spot a turtle in its tank through the fence.
It's also
quite possible to see turtle for yourself out in the water off Fitzroy Island, either when you go snorkelling (ask the staff at the Raging Thunder shack where you get your gear where the best spots are) or on kayak or boat tour.