I went browsing through the prefabs on NWVault but I was unable to find what I was looking for. I'm looking for something with a tall stone wall on one side with equally tall buildings on the other, lots of narrow alleys, something that a procession of revelers could march through and get caught easily in.
Edited to add: I forgot to mention this is for NWN2.
NWN2 doesn't use tilesets the way NWN does. You need to build your area using placables. MoW did a good job creating some areas like the one you described.
You will probably need to compromise your definition of "clausterphobic". While NWN2 has done a good job reducing the "personal space" needed by creature models, they really didn't put a lot of zots improving the models collision characteristics. If you make the area too cramped you're going to have issues with creatures jostling one another and clipping with one another and with the placables around them.
You'll also make it difficult for the players to control their characters in any mode. The character mode won't allow the camera to go back far enough to allow a decent over the shoulder, and the strategic mode will make it hard by making important obstacles vanish to allow for the camera position.
You need to create the illusion of a cramped space. You can't actually make it cramped. I'd point to MoW as the best example of how to do that.
I understand NWN2 handles exteriors differently but I was also aware that Obsidian had contests to get people to build pre-fab areas people could use in their modules. I was just wondering if anyone had created something like that, but I eventually settled on something a little different.
The Just Add Encounter folks make some amazing pre-fabs. I'm using their Ravenloft-ish mountain village with some tweaks. It's perfect for the mood I'm going for.