Back in ancient times (the early 80s) I sold my b/x set to a buddy in order to afford AD&D.
After some time I was asked if I wanted to play in his new badass dungeon. Apparently, he’d made an über-dungeon using all the HD 1 monsters on level 1, all the HD 2 monsters on level 2 and so on. I can’t recall now, but I think it was 15-20 levels of insane battles and traps.
And no, we never finished it. Come to think of it, it was a cool idea, in that weird old school way.
Anyway, that was my first mega dungeon.