For , " The Missing Map " is a classic episode from Season 3. While some lists rank it as episode 39 or 40 depending on the broadcast order, it is widely recognized as a major beat in the season's late-run. [S3E40] The Missing Map Recap

Fans often point out the plot hole of why the Turtles would even keep a physical map to their own home if they wanted to keep it secret.

If you were thinking of a different series, "The Missing Map" is also:

Book #19, The Quest of the Missing Map , where Nancy searches for a treasure hidden by a seafaring grandfather.