For your "Opening scene of Raiders" styled dungeon crawl... I'd suggest Haka'torvhak in Q'barra. From the Grand History of Eberron:
"A dark and ancient force bides its time in the deep jungle, waiting for its moment to strike, for Q’barra is the home of Haka’torvhak—one of the great citadels of the fiends from the Age of Demons and the site of a massive battle between the fiends and the dragons. In the end, the most powerful fiends were bound in the fires deep beneath the city and draconic guardians were left to watch over the place for eternity. The current guardian, the half-fiend black dragon Rhashaak, has been corrupted by the fiendish emanations of his post but remains bound to his duty, though he is determined to use the Poison Dusk pygmy lizardfolk who worship him as a god to ascend to true divinity."
So you have countless wonders and wealth from the Age of Demons locked inside this citadel, all overwatched by a fiendish black dragon guardian and his lizardfolk allies. But at the same time, there's also several fiends locked inside it as well, all capable of corrupting the weak of will.
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For your "sickening" style of creepy adventure location... I'd offer up KhreshtRhyyl, “the Forest of Flesh”, in Droaam... wherein you can find Blackroot Tower, the abode of Mordain The Fleshweaver. There's an Expeditionary Dispatch from Dragon #364 that goes into it. From the article: "Mordain released creatures called skinweavers into the woods. These beasts weave webs, much as spiders do, but instead of producing silk, skinweavers craft their nests using the recycled flesh of their victims, stretching entrails, strands of muscle, and flayed skin between trunk and bough. Many of these are long abandoned, like cobwebs drifting in the wind. Nonetheless, gnawed bones and glistening strands of flesh are a common sight in the forest, and they serve as a clear warning to turn back."
"The skinweavers are one example of Mordain’s ingenuity, but tales speak of skinless wolves, insane elementals, and frenzied beasts formed from the combination of two or more of the creatures found elsewhere in Droaam. Adventurers might find a troll with the voice and wings of a harpy, or a hydra with a medusa’s head sprouting from each of its six necks. Rot scarabs, bloodweb spiders, and stranger insects chitter in the darkness. Vine horrors, oozes of colors never seen in the world beyond, and aberrant dryads linger just off the phosphorescent paths. The laws of nature have been shattered here. Characters familiar with Nature or Dungeoneering may claim that it’s impossible for so many deadly creatures to thrive in such close proximity to one another, and this again is the work of Mordain."