This question was recently bumped by edits: In what order should I read the Robert Langdon books? At first I was going to delete it because it's off-topic for our site, but then I saw the incredibly high view count, meaning that (like many suggested-order questions) it's being useful to drive-by users. I say drive-by because the vote count is so low compared to the view count. On the other hand, the answers are ... not great, especially this and this which provide no support or justification whatsoever for their suggestions. So I'm bringing it to the community: should we delete this question like other off-topic questions, or leave it because it's being useful?
I say this has many of the qualifications that matter to keep it and put a "historical lock" on it.
Aside from being popular (good votes, despite being off topic, and high view count, it's also helpful as a sign post of "Hey, this series isn't actually on topic here!" If people are searching for it and they find this question, they don't need to learn how to use Meta or ask a question and get it closed, first.
In personal experience, I've often found historical lock questions on Stack Overflow and similar sites extremely helpful in figuring out types of questions that are on-topic for that stack. And, speaking from my early days as a user of Stack Exchange, some of the historical locks were actually how I discovered other stacks even existed, since comments pointed towards Programmers, Code Review, Code Golf, etc. Similarly, we could be pointing to Literature (if this would be on topic there. I make no assumptions on that), or some other website.