The description of the building contain a double negative. The last sentence: " No one in the audience is not amazed" is an English grammar mistake. It should be changed to "Everyone in the audience is amazed".
In my opinion, this sentence does not break the rules of English grammar because there isn't a double negative here. The sentence only seems to contain a double negative.
Here is an obvious example of double negative, where the mistake is easy to identify: "Nobody isn't here." The sentence starts with a negative pronoun (equivalent to "no one") and "isn't" is the negative form of "is". To rectify the statement, we need to remove "not" from the verb as follows: "Nobody is here."
The statement mentioned by the original poster above does start with a negative pronoun, but the sentence does not include a verb in the negative form because "not" determines the adjective, not the verb, just like in the following sentence: "The fox refused to eat the grapes because they appeared to be not quite ripe." Although "not quite ripe" can be replaced by "unripe", many authors prefer the former expression whose ambiguity confers a richer meaning.
On the other hand, the sentence "No one in the audience is not amazed." includes the adjective "amazed" whose opposite form "unamazed" seems so weak that certain sources don't even mention it (such as
this one or
this one). The second source in the brackets mentions "not surprised" as an antonym for "amazed". This means one can use "not" to turn an adjective into its antonym, and the sentence "No one in the audience is not amazed" does not include a double negative, only a negative pronoun and the antonym of "amazed". The correct equivalent of "No one in the audience is not amazed" is not "Everyone in the audience is amazed", but "No one in the audience is unimpressed." Technically, one can be impressed or moved but not necessarily amazed.
Last but not least, this is a form of art. The statement "No one in the audience is not amazed" does seem to include a double negative and it does so on purpose. It is impossible for one to definitely tell whether "not" determines either the verb or the adjective, and this ambiguity is a literary technique which can create multiple meanings. Poetic license is often used in literature when a writer ignores grammar rules to induce artistic effects, and (although it only
seems to break the rules) in this respect "No one in the audience is not amazed" is superior to both the sentence proposed by the original poster and to the one suggested by myself.