The above "making of" video regarding the filming of the seven episodes normally referred to under the title "Marco Polo" may be of interest to you; it was to me.
The travelers journey through the arid wastes of vast, empty, spaces--or as I like to think of them, Episodes 3, 4 and 5. That's a tad unjust on Episode 5. After a messenger brings the Khan's command to Polo that he must come at full speed to the Summer Palace, the caravan separates into two groups in order to try to avoid bandits (unsuccessfully, since Tegana was part of the planning party). The "bandit attack" staged by Tegana to seize the TARDIS is pretty good, with Ian and even the Doctor acquitting themselves pretty well in the swordplay (I think--the telesnaps aren't as helpful here as video would be).
Tegana, by the way, stabs his flunky to maintain his ambassadorial credibility. But then the dreary slog resumes (livened with some appealing maps).
But when they arrive at the Summer Palace, we get a whole new genre--Doctor Who comedy. Kublai Khan is a henpecked old man with gout. The Doctor, worn out from a breakneck faced march (ok, horseback journey), is himself hobbling around like a Crimean War veteran. The two old men bond over their ailments, and there's a quicksilver magic in the air that's been missing for too long. Hartnell is quite good at comedy; you can tell even without the video, his voice conveys his irritation, and then, subsequently, his smugness as he realizes he's winning much of Kublai Khan's money (and stallions. About 400 of them):
DOCTOR: My game.When the Empress leaves, the Khan discusses his grandfather Genghis,in such a way as to suggest that he doesn't share the Doctor's enthusiasm for her:
KHAN: You're too good for us at backgammon. Tea?
KHAN: Oh, that is our reckoning?
DOCTOR: Ah, yes it is, sire, yes.
KHAN: What do we owe?
DOCTOR: Er, thirty-five elephants with ceremonial bridles, trappings, brocades and pavilions. Four thousand white stallions, and twenty-five tigers.
KHAN: That's not too bad, so far.
DOCTOR: And the sacred tooth of Buddha which Polo brought over from India.
KHAN: Oh, that? What else? What more?
DOCTOR: I'm very much afraid all the commerce from Burma for one year, sire.
A trumpet sounds)It's pretty much the Timelord and the warlord as The Sunshine Boys. Except they like each other.
KHAN: Oh, the Empress. Hide it, hide it!
EMPRESS: Winning, my love?
KHAN: One wins, one loses, my dear.
DOCTOR: The great Khan is far too modest, my lady.
EMPRESS: You're not wagering are you? You know how it affects your gout.
(The Empress leaves)
DOCTOR: How charming.
KHAN: Charming indeed, and yet there are moments, old friend, when we wish our character were more like that of our lamented grandfather, Genghis. Did you hear of him?
DOCTOR: Genghis Khan? No, I didn't meet him, but I have heard of him. Yes.
KHAN: Oh, he was the warrior of the family. Nothing frightened him. We are the clan of the statistician and the administrator. Oh, she will be furious with me when she finds out what I have lost.
DOCTOR: Oh, then you've lost nothing, sire.
Kublai Khan is pretty laid back about his losses, but accepts the Doctor's "royal gesture" (as the Khan calls it) to play one last game--all that the Doctor as once thus far against the TARDIS.
The Doctor loses, and walks away with a bill of the Khan's paper money as a "consolation prize." He doesn't seem too perturbed though, possibly contemplating a return engagement. Ping-Cho's husband-to-be, an old man she dreaded marrying, dies, and she elects to stay at court for a while (possibly fancying the gallant young rider who brought the Khan's command to Polo). Noghai, Tegana's lord, has encamped outside Peking, and the Doctor realizes that Tegana's plan is to kill Kublai Khan, disheartening his forces, and allowing Noghai to seize the Khan's domains.
The travelers break free, inform Polo, who bursts into the throne room--just in time to duel Tegana while the Khan--great administrator though he is--scuttles for safety. Marco is victorious, the Khan sets him free to go back to Venice--and the Doctor and friends slip into the TARDIS. We get one last joke from the Khan:
POLO: I'm sorry, my lord. I had to give them back their flying caravan.All is forgiven, and the TARDIS is in flight again.
KHAN: If you hadn't, the old man would have won it at backgammon.
For all the longeuers in this story, this is where the show we know is fully present. (And, in fact, the longeuers persist pretty much throughout classic Doctor Who. For every The Dæmons, we get one The Ambassadors of Death--and even The Dæmons has some padding in it, if I'm being candid.) The Doctor is eccentric, sometimes charming, sometimes cantankerous; he's surprisingly competent when he needs to be. Ian is stalwart, the prototype for Harry Sullivan, except much more sensible. Speaking of sensible, Barbara is largely wasted here, but she stands bravely up to Polo on behalf of Ping-Cho, and seems to be captivated by the sights and sounds of an era and place that fascinates her. She's adjusted, enjoying where she can, and fighting where she must. Susan's friendship with Ping-Cho is nicely realized.
As to the guest cast, Derren Nesbitt plays Tegana with a sort of offhand confidence that makes him more intriguing than any scene chewing villain. He's a loyal vassal to Noghai, so deception, murder, theft--whatever. He's got a job to do. Mark Eden is a sympathetic, occasionally histrionic Marco Polo. As the story is framed by his narration, we have intervals of Marco being the viewpoint character, an interesting experiment.