Fireman's castle: inspired by Dante's Purgatory?
The first time I noticed the large Fireman's castle, atop of a steep mountain, I thought DKL might have taken inspiration from Dante Alighieri's Purgatory, the second part of the Divine Comedy. The poet imagined purgatory as a huge mountain surrounded by the ocean and dwelled by the souls who need to purify from the sins committed during their lives. On the top of the mountain he put the Earthly Paradise (Garden of Eden). Incidentally, someone identify the Fireman's castle as the White Lodge, in Windom Earle's words "a place of great goodness [...] fawns gathered there amongst laughing, happy spirits. [...] sounds of innocence and joy filled the air. [...] it rained sweet nectar that infused one's heart to live life with true beauty." The description matches the Garden of Eden pretty well.
There's a strong connection between Twin Peaks and Dante's Divina Commedia. Dale Cooper being Dante obviously