The problem with establishing where Marco Polo went is made greater by
a. The lack of contemporary Chinese records describing what he did
b. The nature of his book ("Il Milione" or "The Travels of Marco Polo") which mixes material from all sorts of sources and lacks detail of dates, distances, stages etc.
With other "historical personage Connections" we have tried wherever possible to establish exact buildings and detailed locations inside cities/towns (eg Napoleon) but have also assumed that if a person visited a location in historic times then, what constitutes the "Historic town" etc in modern times, would have been included (eg Humboldt). I think this latter approach is fair IF we definitely know that Marco Polo visited a place and that he wasn't just describing a place visited by others, stories he had heard etc.
As far as I am aware the only places we KNOW that Marco Polo visited were
a. Venice - he was born and returned there
b. Acre - He received his credentials and picked up his 2 "Friar" travelling companions there
c. Jerusalem - He visited to pick up the holy oil following Kublai Khan's request to his father Niccolo on his own earlier trip
d. Beijing - He stayed in China for c 17 years and visited both the summer ("Shangtu" or better known as "Xanadu" which is on China's T list as a ruined city in Inner Mongolia) and winter residences - the latter at DaDu is approximately where Beijing is today. The "Forbidden City"/"Imperial Palace" etc is however primarily Ming and Qing and is not in exactly the same place as Dadu. The inscription documents state :- "The Ming retained the location of the Imperial City as well as that of the line of ramparts east and west of Dadu, but the north and south ramparts were moved, creating a rectangular city measuring 6,650 x 5,350 metres". I think this is enough to state that (at least some of?) the inscribed area of the "Imperial Palace" is within the "Dadu" visited by Marco Polo.
e. Istambul (Constantinople) - he certainly passed through on his return to Venice. Many of the inscribed sites post-date his visit but the walls are included so I think this is valid
Marco Polo was imprisoned in Genoa in 1295 (and dictated much of his "book" there) but, as its WHS inscription is limited to specific named Palaces built from the 16th to 18th centuries, I don't think we can count that.
He certainly travelled the "Silk Road" but, whatever "Dr Who" says, I know of no evidence that he visited Mogao caves!!