In the Tomb of Annihilation adventure you have to find a lost city in the middle of the jungle in order to lift a terrible curse created by the Archlich Acererak. I mean, it’s a perfectly fine premise. A terrible adventure as written but a fine premise.
But here’s a few more campaign ideas that would be great for such a setting as Chult:
Claws & Teeth & Ultima

(Image: James Gurney – dinotopia)
The dinosaurs, long domesticated by Chultans for all sort of uses, spectacle not the least, have recently started to manifest dangerous magical powers! What sinister power is behind this source of mayhem? Or is it rather linked with the long neglected primordial Ubtao, the so-called Father of the Dinosaurs?
Extinction: the Elemental Evil’s Meteor
Spewing volcanoes, tumultous seas, devastating earthquakes and toxic mists, all at the same time and getting worse! And a new, angry star has appeared in the sky. It’s the end of the world. Unless you defeat the four elemental cults that together are summoning Elemental Evil.
The Crash of the Star Princess

(image: yuchenhgong)
Of the surviving Netherese ancient artefacts, few are more precious or sought-after than the Airships. There’s only a handful in the world and now one of them have fallen from the sky and woe! of all places it fell on thrice-accursed Chult! The race to be the first to find it (and to get it to fly again) is on!
Tombs of the Slumbering Sorcerers

(image: The mud sorcerer’s tomb – paizo)
Centuries ago, a group of aristocratic Mezroan sorcerers foresaw the demise of their city and its empire. One of them, Piyyat the Unscrutable, proposed a plan so they could come back after the disastrous events had come to pass. And so the sorcerers each prepared their own tomb where they could slumber undisturbed. And they hid their riches with them…