In the end of Heaven Sent, The Doctor appeared in the middle of a desert,
on Gallifrey.
Why did the Time Lords leave the confession dial,
with the Doctor inside,
abandoned there? It would make sense to store it somewhere instead.
In the end of Heaven Sent, The Doctor appeared in the middle of a desert,
on Gallifrey.
Why did the Time Lords leave the confession dial,
with the Doctor inside,
abandoned there? It would make sense to store it somewhere instead.
It wasn't "stored" there.
When he broke through the wall, a portal opened into this part of the desert. Only when the portal closed, did the dial appear out of thin air and fall to the ground.
There is no evidence that the dial was visible as a normal looking physical object anywhere whilst the Doctor was trapped in it. For all we know the location of the exit portal is random. It is apparent that the designers of the trap had no clue the wall would ever be breached and likely had no specific plan for it.
Remember that him spending 4.5 billion years inside there wasn't originally part of the Time Lords' plan. To understand why he stepped out of it into the Gallifreyan desert, we need to think about what they envisaged was going to happen.
Presumably they expect him to give in to the pressure and make his confession within a matter of days. What would have happened then? He knows he didn't time-travel to arrive in the Heaven Sent castle, and the reason he actually turned up on Gallifrey, at nearly the end of the universe, when he emerged was because he'd spent so long in there ("I came the long way round"). If he'd emerged billions of years earlier, after spending only a few days inside, he would've been in the same time zone he started in. Presumably then some time-travel process would have been triggered to take him to Gallifrey, perhaps to a holding cell somewhere.
But because he spent so long in there, he was already in Gallifrey's time zone when he emerged, so no time-travel process was triggered, and he just stepped out into the desert. Perhaps that spot, on Gallifrey at nearly the end of the universe, was actually the same physical location as Trap Street, London, Earth had been so many billions of years before!