Soldato
Capaldi is fast becoming my favourite actor to play the Doctor.
My view on this episode:
The Doctor was transported inside his own confession dial by Me (who is indeed the hybrid). Bigger on the inside etc. The skulls were all the Doctor's skulls. He has not moved anywhere in space but has obviously lived several mission years. When the Doctor eventually escapes he is on Galifrey.
I'm not that clued up on Doctor Who history but in the episode where Galifrey was sent back to the time lock wasn't there something about a diamond being used to connect Galifrey to Earth? I suspect that the whole point of the Doctor being sent inside his confession dial was for him to break through the diamond and once again free Galifrey from the time lock. So it has been planned and engineered by the Time Lords.
But I have no idea what that circle with the arrows pointing to it was for.
It was to remind him that you can write in the sand as he never noticed it after stepping out of the teleporter, he just realised that it was a very old building due to the "sand" being stone dust.