I'm planning to start an Old School Campaign next week, for players who have mainly played D&D 3.0 and 3.5. I'd like them to play a real classic old school module. I have both B1 - In Search of the Unknown and B2 - The Keep on the Borderlands, which are extremely early published modules. Is there anything earlier than these, maybe something that was included with the White Box?
If you look at
It seems to be that Palace of the Vampire Queen was the first somehow published Adventure in 1976.
Edit: Here are some more details about it: It's the first D&D Module ever published, but not the first TSR one. There was also a scenario that was published earlier in the Blackmoor supplement.
As discussed on the acaeum werbsite, The first D&D module was Palace of the Vampire Queen, the first TSR module was G1: Steading of the Hill Giant Chief, while the first scenario was The Temple of the Frog which was included in Supplement II, Blackmoor. Vampire Queen was distributed by TSR and went through six printings in a couple of years. Not called a "module", it was labelled "Dungeon Masters Kit Number 1".
Dungeon Masters Kit Number 2 was "Dwarven Glory" and the third and final DMK was "Misty Isles", all by Pete and Judy Kerestan (Wee Warriors) and all predated G1.