I have heard presentations on lunar lava tubes that estimated the temperatures of the ground surrounding them as being well below zero. An article in NASA Science News says this:
Once you get down to 2 meters under the surface of the Moon, the temperature remains fairly constant, probably around -30 to -40 degrees C.
But this graph of measurements taken on Apollos 15 and 17 paints a very different picture:
The above is from Ch. 3 of the Lunar Sourcebook, page 12 of 34. All measurements taken showed rising temperatures with depth of about 1 oC per meter. The largest known lava tubes on the Moon have skylights revealing depths of 100 m, so if that rate of temperature increase is taken, then the floors of such tubes should be about 80 to 100 oC warmer than the temperature near the surface, which means something like 60 or 70 oC. I've never heard any such figures talked about.
So, is there a cooling mechanism involved with these tubes? I wouldn't have thought so, being in a vacuum and only open to the surface through gaps that are probably very small relative to their full size. Why this apparent discrepancy?