What is the Best Beginner Module?

Which adventure would you say is the best published adventure module for beginning players and characters?

There are rules for this survey:

• One module. Not a series, not your best three. One module.
• The module must have been intended for Pre-89 D&D editions, or one of the clone/simulacra or various compatible things.
• The module must have been published as a physical book.
• Naming a module you wrote, proofread, laid out, etc is not allowed. Don't be lame.

So name it, and say why you chose it.