RA is a true megadungeon, at least the 3E version was. Like Dizzy, I got the S&W pdf version but haven't looked it over to compare yet. There was a bit of background, in order to explain Rappan's existence, but very little overall.
Back to the original question, I ran some homemade ones back in the 1980s but I'm afraid I haven't found a group interested in megadungeons; either for me to run or to play in.
I'd really like to run a full cleanout of either Tegel Manor or B4. Oh well!
DM (Good at missing the megadungeons) Mike