This is absolute peak. The Third Doctor and Sarah Jane land on a lesbian hippy art commune... on an abandoned oil rig... which is floating... on a planet with nothing on it but sea... and they're menaced by eldritch horrors. What a scenario! There was such a genuinely menacing buildup in the first two parts and the characters were all really likable, which made them literally dying via crying hit all the harder. And The Gulf itself is such a good villain! I definitely headcanon it as a member of the Pantheon (God of Sadness maybe?)

If that all isn't enough to convince you to give it a shot, the Doctor quotes Jon Pertwee's "I Am The Doctor" song whilst psychically beating up the baddies. I was squealing as soon as he said "I cross the void beyond the mind". Nuff said.