I'm not giving away any real spoilers, but I do have info on two of the locations for the last few episodes of the extended Series 4+ with David Tennant.

I have it on authority that part of the filming took place in caves (alien planet?) outside of Cheddar. And, that they've done some filming in a steel mill (alien space ship?).

I don't know for which episodes these were: Waters of Mars or Ten's two-parter swan song?

I've been avoiding spoilers at all costs, but these aren't really spoilers, 'cos I don't know which episode they're for, and...well, Dr Who and alien planets/spaceships, that's pretty much a gimme', yeah?