I was recently remniscing with an old friend about the earlier adventures we had played that we had enjoyed most - the Dragonlance campaign, The Scourge of the Slave Lords, the Temple of Elemental Evil (both times), the Desert of Desolation, Queen of the Spiders... ah, good times. An eternal thank-you to Tracy Hickman and Gary Gygax for the profound effect they've had on my gaming life.
Anyway, we both agreed that probably the best campaign we'd ever run was the second Ravenloft adventure, The House on Griffon Hill which was run simultaneously with the original I6 Ravenbloft module as a series of dream sequences... when the PC's went to sleep in one they awoke where they had gone to sleep in the other and back and forth, with the 'dream' adventure giving valuable clues to the shared history of Griffon Hill and Castle Ravenloft.
It occurs to me that we haven't really seen a gothic horror-type AP. Rise of the Runelords had plenty of what I consider to be 'modern horror' (serial killer Skinsaw Man, in-bred hillbilly Kreeg Ogres, the Wendigo and canibalism 'cabin-in-the-woods' style) and it was bone-chilling, but nothing that gave a nod to the classic horror we all grew up on. I'd love to see something done with that, especially by the quality writers at Paizo.
There's also the Curse of the Golden Spear trilogy of adventures set in the Japanese horror setting of Kaidan by Rite Publishing - exploring the ancient ghost story tradition of feudal Japan. If you're looking for some truly creepy encounters in a very cursed land - check it out.
You could also check the free one shot adventure set in Kaidan, called Frozen Wind. Rite has recently released 2 other one shots as well, though not free ones.