Tomb of the Serpent Kings
People keep asking for "beginner" dungeons. Everyone can name "classic" dungeons - Tomb of Horrors, Barrier Peaks, Ravenloft, etc. - but in order for those adventures to make sense, there needs to be some sort of introduction.
It's like all the adventures we have are Bach concertos. People keep writing amazing works of staggering genius, but someone needs to write a book on how to play the piano.
I had the same questions, and since I couldn't find anything satisfactory, I decided to write the kind of dungeon I would have loved to find. I wanted to write the best basic OSR dungeon for beginners that I could, and I also wanted to show the design process.
If you like this dungeon, please share it, tell people about it, print copies and leave them lying around local game stores, or email this post to friends who have "always wanted to try D&D but don't know where to start". The entire thing is and always will be free.