The Thorsborne Trail on Queensland's Hinchinbrook Island is a delightful walk through some of the most unspoilt island rainforest in the world. Hinchinbrook Island has quite rightly been protected as a National Park since 1932, and it's Australia's largest island National Park (Fraser Island is a much bigger island, but it's not all National Park).
To maintain the pristine nature of Hinchinbrook Island, access to the island is very restricted, so don't plan to just turn up and walk the trail; you need to get a permit from the park rangers and sit through a video all about minimal impact bushwalking before you're allowed to hop on the ferry to the start of the trail. I was lucky and managed to get a trail permit within a day of applying, but at busy times of the year you may be in for a very long wait.
This restriction is an excellent idea, as it means Hinchinbrook Island is an untainted paradise. The Thorsborne Trail follows the east coast of the island in a southerly direction, so the sea is never very far away to your left. Stunningly beautiful palm-fringed beaches are a recurring theme, and the campsites are hidden away in the rainforest within spitting distance of some of the most luscious island landscapes you're likely to see. It's beautiful, if a little wet, though it would be pretty unfair to expect anything else from tropical rainforest.
There is one downside, though, and it's pretty a grim one. Hinchinbrook Island is infested with rats, particularly the mosaic-tailed tree rat Melomys cervinipes, and the white-tailed rat Uromys caudimaculatus. These guys know how to get a free meal, and it's by hanging round the campsites, stealing food and ripping into tents; the advice, therefore, is to lock your food in the rat-proof boxes provided at some sites, and where there's no box you should hang up your food bag from a tree. They'll even rip into your tent to eat your toothpaste; these guys mean business.
Add in the sandflies and mosquitoes, and this is no walk for the squeamish. But if you're fine with the great Australian outdoors, this is a lovely walk, especially if you manage to catch it when it's dry.