There are three D&D campaigns on my mind these days. Two that I want to run and one that I want to play.
The latter is what I think of as the classic Greyhawk campaign. In the mid-1980s, several early adventure modules were combined into compilation "giant" modules, with new material that tied them together in a single narrative. An "adventure path", to use the modern term.
It starts with T1-4 The Temple of Elemental Evil. The original T1 The Village of Hommlet is probably THE iconic 1st-level adventure module for AD&D, in much the same way that B2 Keep on the Borderlands is for Basic. Like B2, it reproduces on a small scale the
traditional "megadungeon" format. You have a multilevel dungeon and a nearby outpost of civilization where the PCs can resupply and sell loot. In B2 it's Kendall Keep and the Caves of Chaos; in T1 it's Hommlet and the ruins of the Moathouse.
Because I want to play it, I haven't read ahead, so I can't talk much about T2-4. Next up is A1-4 Scourge of the Slave Lords. The A-series were originally some very loosely connected tournament modules from the late 70s. The compilation version tied them more closely together, and added a new prologue that picks up directly where The Temple of Elemental Evil left off. At this point, the PCs are probably around levels 6-8.
More new material foreshadows the 3rd and final module of the series, GDQ1-7 Queen of the Spiders, which a 2004 Dungeon survey ranked the greatest module of all time. Even before the giant modules came along, the G and D series were already a linked series―the first one, published back in 1978. It's probably best known now for introducing the Drow. In 1980 Q1 Queen of the Demonweb Pits added a final chapter: taking on Lolth herself on her home ground in the Abyss.
As before the compilation "giant" module version added connecting material. I'm not sure what though, since I've tried to avoid spoilers.
So that's the Great Greyhawk Campaign: start out a typical level 1 peon in a typical dungeon crawl, and finish up around level 14, having punched out a demigoddess.
For the love of Celestia, somebody run this for me!