First dungeon you explored as a player-character or ran as a DM?
The first true dungeon that I remember was Tegel Manor. I played a thief named Embrace Nothingness. He eventually did live up to his name and died there.
The first dungeon I ran as a DM was in 1993. It was home-brew dungeon leading to the under dark. It had giant rolly-polly or pill-bugs in it, plenty of drow and a underground freshwater bay.
The dungeon and nearby city are still in by home-brew campaign setting.
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