Doctor Who: 10 Most Poetic Moments
9. The Stint In The Confession Dial (Heaven Sent)
Driven half-mad by his grief after witnessing Clara's death at the hands of the Quantum Shade, the Doctor wakes to find himself inside an abandoned castle, being pursued by a great hulking creature in a veil. It's an episode that begins in classic sci-fi horror fashion, and as the nature of the castle and the creature inside it is revealed little by little, we come to realise just what's happening.
The Doctor's confession dial - which had been knocking around for quite some time at this point, with very little by way of backstory - is, in fact, a prison of sorts, designed to hold him in a sort of purgatory, and the Doctor begins punching at a substance he describes as "harder than diamond", believing that the TARDIS is behind it.
Working out from the handful of inexplicable signs of life that he's in a loop, he sacrifices himself to restart the cycle, leaving only the cryptic message that he himself discovered upon waking.
Upon emerging victorious, we learn that the Doctor spent four and half billion years inside the confession dial, slowly punching his way out and thinking of Clara all the time.