The one where Kronos destroys Atlantis...
So why did director Paul Bernard leave the shot of the Minotaur out of the episode 5 cliffhanger? Surely such a reveal would have been more powerful (and scarier?) than simply zooming in on Jo's terrified face? A similar cliffhanger boob happened with The Sea Devils episode 4, when just leaving it a few seconds longer would have made it so much better.
The Minotaur (played by a pre-Star Wars David Prowse) isn't so bad a design either, certainly not as poor as the one seen in The Mind Robber (which looked more like a troll than a bull). Prowse's power and strength are used to the full as he charges around smashing into things, at one point lifting Hippias above his head and hurling him through a sheet of Bacofoil. The silver foil is actually supposed to be a pane of glass (not sure why) and, surprisingly, kills Hippias. The Doctor joins the scene and, in typical Jon Pertwee style, uses his red cape to taunt the Minotaur, as if bullfighting. Finally, and somewhat inexplicably, the Minotaur charges into a wall and smashes it down, seemingly killing itself into the bargain, but also revealing the true crystal of Kronos. The Minotaur is all over in less than three minutes!