I have a business visa for Germany but my business trip got cancelled.
Can I travel as a tourist using the same business visa for the same dates to Germany?
If yes, do I have to show the same documents I used the for business visa during immigration or my new travel itinerary as a tourist?
Answers to earlier questions like Can I use my Schengen visa for a completely different purpose and entry point?, Should my first trip be to the country which issued my Schengen Visa? and Use of unused Schengen visa to travel to Switzerland provide a lot of details on the validity of the visa.
Regarding the document question, you can always (theoretically) be challenged to document all relevant facts at the border, very much including the purpose of the trip. Since your business trip got cancelled, it's obviously not the real purpose of any trip you would make now. Suggesting that it is the case or presenting an itinerary you do not intend to follow could even be considered deceptive.
In other words, if you are asked what you want to do in the Schengen area, you should not lie. A non-existent business meeting or event cannot be a valid purpose and without a valid purpose, you should be denied entry. Always present your real itinerary.
