Be sure to check out Fulcanelli's 'Mystery of the Cathedrals' for an alchemical interpretation. I believe the pdf is easily found online. I just found this interesting article about it, which i'm reading now.
The Sword in the Stone: Fulcanelli reveals the Secret of the Cathedrals | Vincent Bridges´ Legacy
I couldn't find much online for this yet, so i'll just have to copy this random fb post I found from an unknown author:
"Rosslyn Chapel frequencies, the ark of the covenant, earth measure and 8:9 ratio.
Below I will list some frequencies that if tuned to can assist in tapping into the earth's resonance and Rosslyn Chapel. These can be used for musical tuning to bring about a healing resonance one can meditate to.
Rosslyn chapel was built in the 15th century by William Sinclair. The Sinclair family (who claims blood ties to the Merovingian kings of France who descended from Mary Magdalene) founded the Grand Lodge of Scotland in 1736. Sinclair was said to have arrived in America years before Columbus. For what reason? Here's a thought. There's said to be a grand treasure on Oak Island as you may know, known as the money pit. Oak Island is off the coast of Nova Scotia which translates to "New Scotland." Scotia being the the daughter of the pharaoh Ramses II. She was the queen who founded Scotland. Do you smell the Ark of the Covenant in this aspect of history along the thread of Sinclair-Scotland-New Scotland Oak island treasure? The Ark box resonates at 131 hz (if you base the 2.5 cubit length of the ark box on the 20.63 inch long Royal cubit). If you divide the internal length of Rosslyn Chapel by the speed of sound you get octaves of 131 hz, the same frequency as the ark box wavelength resonance. The choir room in the chapel also has octaves of this same 131 hz resonance. If you convert the amount of time sunlight takes to reach earth into hz you get octaves of 131 hz as well. The stave angel is shown to be holding what's figured to be the A note, B note and C note. 131 hz falls under the note C. The width of the Ark box falls under the note of A. Unsure so far of where the B note is in the chapel or ark box.
Rosslyn chapel is 72 feet long inside and 81 feet long outside. 72/81 is the same ratio octaves as earth circumference/speed of sound. Also same ratio octaves as earth circumference/Planck length. This ratio in its most broken down state is 8 over 9.
Both the Rosslyn chapel and the earth’s circumference relative to speed of sound have this 8:9 ratio but the other common thread is that both are expressing the ratio of the inside compared to the outside. Obvious with the chapel given we’re talking internal length compared to external length. As for the earth expressing this inside

utside ratio we can see it like this, earth’s internal ground temperature is avg 68 degrees F causing the speed of sound to be 343-344 meters per second. So 344 meters or so is the “inside” and the outside is earth’s circumference (approx 40,042,754 meters). The circumference divided (outside) divided by the speed of sound based on the internal temp=octaves of 0.8888888 hz and 0.88888 is the ratio 8/9ths (given 8 divided by 9=0.88888). Also an octave of 0.111111, 0.2222222 and 0.4444444 hz. The Planck length (threshold measurement between matter and quantum realm) is octaves of the speed of sound so therefore the equation relative to earth’s circumference brings the same 8:9ths octaves when you put the Planck length in comparison to earth’s circumference.
To summarize, 8:9ths ratio is the ratio of earth’s circumference relative to the speed of sound as well as the ratio between the internal and external length of Rosslyn Chapel and the common thread between the two being 8:9ths being the ratio between the inside and the outside. As I’ve explained before, if you divide the speed of sound (343-344 meters per second) by the internal length of of the chapel you get octaves of 7.83 hz which is the Schumann resonance, aka the heartbeat of the planet.
Below is a visual of what the ratio 8:9ths weaves. That general design is made manifest as an energetic grid of resonance in Rosslyn Chapel given the ratio of its internal length to its external length, and across the world as a sound grid and a Planck length grid all due to the law of sympathetic resonance. If you flip this ratio inside out (9/8 instead of 8/9) then you get octaves of the auspicious number 144. Earth circumference sound frequency (227.555555 hz) divided by Ark box 131.072 hz=octaves of exactly 0.144. 131,072 is the 18th number in the binary sequence (1,2,4,8,16,32,64 etc)."
I understand much of that info probably deserves to be in another thread, but it does relate to the question of cathedrals and not entirely out of sight of what the Cathars were about.