Underground Adventures, Depth, and Temperature

[Daigoro]

In the dwarven agricultural thread we thought about this a little.

I think that's a broad rule of thumb, for all other things being equal. But to see a real world example of how temps might vary, these two graphs give a good idea.

Page 9 of this PDF.
This webpage.
And this abstract talks about the effect of subterranean waterflow.

I'm not sure air would have such a great effect, as it doesn't have as much thermal mass as rock, although significant honeycombing would break up the conductive paths for thermal flow through rock.