@pink-x-eye thanks for sending me this!
I'm not familiar with this sort of AU (though I do have some familiarity in the doors thing via the magnus archive) so I don't know the conventions. But I think it does lend itself really well to Adansey. So, Five Fun Facts for an Adansey Magic Doors AU:
Tying it to canon, I think the recurring thing would be that it has to happen at 6:21 or june 21st or on the 6th and 21st of each month. The door phenomenon would have been happening to Gansey since his near-death experience, but Adam's only been experiencing it since he lost his hearing.
2. Adam tends to open his doors to quiet scenes and empty spaces. Gansey's runs the gamut and is eclectic (his glendower journal could be a doors journal in this.) But they end up meeting in the middle at a grand library. (I'm imagining like the Clementinum National Library in the Czech Republic or the Royal Portuguese Cabinet in Brazil)
3. Adam would be jealous that Gansey's been able to use the doors so long. Likewise, he's concerned that Gansey hasn't thought through all the logistics (what if we don't wind up back where we started? what if we end up somewhere dangerous?) Though, he is enamored with Gansey's journal and they go through it together, slowly realizing that they've visited many of the same places at many of the same times without seeing each other -- the two separate travel styles being very thinly separated. Think, Adam's on the patio of an empty restaurant looking out at a beach, hearing the noises of celebration only to find out Gansey was at the party and the house had emptied for the celebration but moments earlier.
4. Every time they open the doors after that, they expect to see each other. Sometimes they'll leave little notes in places they think the other person will look, just in case they miss each other. They'd find them and reply to them at the next location. If you've ever seen the movie Every Day, Every day (or read the book), I think it'd be a similar sort of thing to the emails in that, especially if/when they have a disagreement and need some space.
5. The Au/Fic would have to end on Gansey opening the door that leads to Adam's room and them settling any issues and deciding to see what happens if they don't go back through the door before the end of the day so that they can start traveling together.
Send Me an AU and I'll tell you 5 fun facts on what I'd write.