As far as I can tell, thre's no real world architecture influences in there, but defintively some from fantastic/sci-fi descriptions of 'otherwordy' places with weird angles, oddly-shaped doors and the like (plenty of examples in 1920-30 texts, Lovecraft among others).
My take would be Bethesda design with literary/arts influences. Thye didn't deisgn that in a vacuum.
Outside, some Hindu Indian and Maya, Inca, a hint of religious islamic with a splash of unearthly topology.
Inside, islamic from the Mahgreb (ceiling treatment and horseshoe arches, not to mention the censers).
The asymetrical "spiderweb" doors might be some Subsaharan African design with a liberal gush of Late Evil Overlord.
As everyone knows, unspeakable horrors from beyond the physical dimensions are indissociable from http://images.google.com/images?q=%22baby%20penguins%22.
Everybody knows that http://www.pingu.net/uk/index.htm are bent on world-domination and have been running Europe from Switserland ever since 1986.