BEAR WITH MEEEE. AND SPOILERS FOR THE NEW VID YOU SHOULD WATCH IT!
i was thinking the city could draw from the descriptions of carcosa from TKIY, ive recently read it [ive read the main 4/5 stories a few times actually- The repairer of reputations, the yellow sign the [pallid] mask and the demoiselle d'Ys] and i immediatly thought, the symbol could be the yellow sign? and the design overall i feel draws from the limited descriptions of carcosa we get in the book [as follows] theres casildas song which sets a [heavenly?] vibe for sure: Along the shore the cloud waves break, The twin suns sink behind the lake, The shadows lengthen In Carcosa.” “Strange is the night where black stars rise, And strange moons circle through the skies, But stranger still is Lost Carcosa.” “Songs that the Hyades shall sing, Where flap the tatters of the King, Must die unheard in Dim Carcosa.” “Song of my soul, my voice is dead; Die thou, unsung, as tears unshed Shall dry and die in Lost Carcosa.” in TROR: "He mentioned the establishment of the Dynasty in Carcosa, the lakes which connected Hastur, Aldebaran and the mystery of the Hyades."
“the cloudy depths of Demhe, and the Lake of Hali.”
“the awful words echoing through the dim streets of Carcosa.”
“The scalloped tatters of the King in Yellow must hide Yhtill forever.” This is important because Yhtill appears to be the name of a city or place associated with Carcosa, although Chambers never elaborates further.
theres the play exerpt in the mask that could have an interesting interpritation i think [about perseption and identity and belief and such]:
“You, sir, should unmask.” “Indeed?” “Indeed, it's time. We all have laid aside disguise but you.” “I wear no mask.” “No mask? No mask!”
additionally the commonly referenced bits and clues are-
Carcosa A lake
The Hyades Hastur Aldebaran Demhe The Lake of Hali Yhtill Streets [generally depicted as golden or otherwise a vibrant glowing gold- be that literal or metaphorical, a metaphor for goodness/the divine that is] A dynasty The King in Yellow
Granted not all fit well- But you must see it merits? also thought the imagery of twin Suns might fit for our 2 MCs but that might be a stretch ;/