The BEST longfics you've read? Your forever favourites?

I'm interested in reading peoples favourite longfics. I have my own list of oneshots and short multichapters that I swear by and am always coming back to reread, but longfics are more uncharted territory. I rarely venture into anything over 20k.

So: I'd love to hear your recs for anything, say, 50k or more, and I won't complain if the wordcount hits a million.

If you have a long list of favourites and want to narrow things down, then I don't usually tend to go for X Readers, but if you've got a simply stunning one, please! Throw it my way! I love an eventually happy ending and endless whump isn't really my thing - but hey, I'm asking for your favourite favourites, so if your favourite favourite is a sad ending whumpy miserable mess, link it. I go crazy for a well-written Hunger Games crossover too.

As for my own recs to you all, here are some favourites:

The End of the World by FernWithy. Hunger Games, 110k, I'd say you can read this blind, and completed. This is by far the best Haymitch's Games fic I've ever read. There are excerpts from it that I'll never be able to get out of my head. This fic has a bitter ending, but I haven't read any of the sequels (I didn't know they existed until now?!), so I can't say if that changes with those.

Both instalments in the Skeleton Crew series by RecklesslyCaffeinated. Undertale (AUs) with Classic, Fell and Horror Sans. The first fic is 90k and the second 120k. I actually believe the author uploaded the final chapter to the second fic today. This is one on my short list of guilty pleasure x Readers, and it's worth it. You won't get Sans Undertale as he was in the game, but you will get a very enjoyable story.

Echo Answers by reedroad. Attack on Titan, 240k, fandom blind friendly, completed. A no-titans paranormal AU, which I wouldn't normally read, but this fic is INSANE. Do yourself a favour and give it a shot. It's so good. The EMA is somewhat background but there. I will say that this fic is rated teen but personally feels more mature/explicit.