Since most of the work is still ongoing for my own world, there are just a few I've got done...mostly from when I sat down to answer a pressing question: "So...why psionics? Especially since I prefer 'psionics are different'."
1) The Fallen Sentinel of the Holy City
While historical texts and legends are divided over precisely where the Holy City once lay (save that it was clearly somewhere in the Wasted North), who it was holy to, and what purpose the Sentinel served, it is clearly there. An emerald statue of truly immense proportions, only the top of the Sentinel's hill-sized head and a single massive fist protrude from the blackened soil, resisting any attempts to be divined or carved, despite the clear tool marks from its creation.
2) Deathchoir Forest
Neither a wonder (being a natural formation) nor a forest, this hundred square miles of inhospitable beauty still warrants mention. Forming a natural barrier between the warring tribes of Hlaidet Isle, labyrinthine passages, caves, and semi-underground rivers cut their way through limestone pillars, on average thirty feet high, eroded to razor sharpness by the countless typhoons that rip across the island. There is not enough level ground in the entire area for a gnome to put one foot flat on the ground, and a single mis-step could skin a limb or sever an artery. Though the monstrous crocodiles of the caves are primarily sluggish, the belligerent and man-sized eels pose a great danger to tribal raiding boats plying the rivers. While eerie, the keening wail caused by wind playing over the limestone is the least dangerous feature of the landscape.
(Heavily inspired...by which I mean stolen...from the Madagascar tsingy lands.)
3) Heretic Rock
Most assume the massive plateau in the Wasted North is simply a peculiar mountain, perhaps moved there by magic. Nearly four miles high and thirty miles across in any direction, erosion markings turn its silhouette into a vague impression of a fist, raised to the Heavens in open rebellion. This is widely believed a curiousity, as few would dare penetrate the Waste to learn its secrets - it is widely known nothing grows there, and all life is predatory or worse. And who would ever believe that not only does the plateau feature into the creation of the Waste, but the entire structure was fashioned by mortal hands?
4) Web
Most residents of the continent of Siorhal are aware of The Deeping, a seemingly endless chasm (though only a dozen miles long), the bottom of which is occupied by a lightless sea and the walls of which are riddled with tunnels leading into all parts of the Lands Below. Hanging half a mile beneath the surface, suspended from immense adamantine cables, is a city the few remaining inhabitants call Web.
Constructed by the elves as a racially 'neutral' citystate, the cataclysm that created the Waste led to its widescale abandonment and the slow withering of its High Magic wards. No longer censured from its borders, the vile things of the lightless world set to slaughter. The few who remain in the city are descendants of those too poor to leave in ages long past, a ragged and desperate sub-breed of humanity scratching out survival. However, there are no greater guides to the Lands Below anywhere in the world, and none better trained in fighting the horrible denizens of those endless tunnels...and so, adventurers still make the treacherous descent.