Cruise to the Great Barrier Reef. Day boats run to outer-reef pontoons and coral cays with snorkeling, glass-bottom boats and optional intro dives — non-swimmers are well catered for. The outer reef has the best coral and visibility; pontoons like those at Moore or Agincourt reef suit families best. Book a day with good weather if your dates allow flexibility.
Ride the Kuranda Skyrail and Scenic Railway. The classic loop: glide 7.5 km over rainforest canopy by cableway to the village of Kuranda — butterflies, markets, a koala park — then return on the historic railway past waterfalls and gorges. The combo costs around A$120–A$130 ($85–$90).
Go north to the Daintree and Cape Tribulation. Day tours cross the Daintree River (crocodile-spotting cruises included) into 180-million-year-old rainforest, where the forest meets the reef at Cape Tribulation's beaches.
Swim the Esplanade Lagoon. Cairns' beachfront is mudflats, so the city built a huge free saltwater lagoon on the Esplanade — the social heart of town, open year-round and safe from jellyfish.
With another day, the Atherton Tablelands deliver a waterfall circuit (Millaa Millaa is the famous one) and curtain fig trees, or take the short ferry to Green Island or Fitzroy Island for a lazier reef-and-beach day.