Keys Of Marinus for me felt like a very long journey.

I'd treat each location as a separate but related adventure and give yourself a break between.

Seen as a connected mini arc it works better than trying to sit through the whole thing in one go.

I prefer the shorter Hartnell stories like The Sensorites, The Romans or The Aztecs myself (though The Ark has one lovely little bridge section).

Part of me is sort of glad I don't have to sit through The Daleks' Masterplan due to BBC incompetence.