The only written record of his journey includes many fantastical embellishments that could not have been true (ie descriptions of animals that have never existed). There is also no confirming documentation of his presence in Asia from historical documents from that area of the world, which you think there would be considering some of the things he is supposed to have done while he was there.
I'm not surprised that the stories were embellished, they were to entertain his cellmate, not provide an historical record.
However his stories are more accurate than other Western records of the time, and include specific details of currency, salt production etc. that were not known in the West or the Middle East.
Edit: maybe Vasco Da Gama should also be here as one of the famous travelers?
(ahem, I of course scored a 5 )