The Moonbase was a four-part series broadcast just before I was born in 1967. It is set entirely on the Moon, at a base from which the world's weather is controlled; the Doctor and his three companions (Ben and Polly from 1966 and eighteenth-century Jamie) arrive in time to avert the conquest of Earth by the Cybermen their second appearance after The Tenth Planet. It's not easy to watch, because episodes 1 and 3 are lost; in the end I played the soundtrack off my Lost In Time DVD while flicking through the BBC photonovel, and then watched episode 2 and 4 directly.
I have to differ with the fannish consensus that this is better than the Cybermen's previous outing. I found the Cybermen more difficult to understand, the plot implausible even making allowances for scientific hand-waving - the base commander ought to have been shot for his attitude to security - and the direction seems to consit of lots of actors standing around waiting to say their next line.
On the other hand, the look of the sets is pretty good; two years before Armstrong and Aldrin, they do a decent lunar landscape and setting. The incidental music is great. And Troughton is brilliant, though Ben is annoying, Jamie comatose for much of the story, and Polly is repeatedly patronised - noticeably the only female character, told to go and make the coffee, told she can't take part in the final attack as it is "men's work". I don't find myself especially mourning the two missing episodes.