Yesterday I brought you to the conclusion that lava tubes look like good locations for manned lunar bases. But before I tackle the thorny problem of finding lava tubes in the first place, I feel I ought to give some idea of scale of these lava tubes. I said that you could put a village down inside the largest ones. This was probably an exaggeration, although there's at least one rille 3 km wide. Here's some example data:
A small lava tube might be 20 m under ground, 20 m across and 15 m high.
A large tube might be 500 m under ground, 300 m across and 100 m high. So pretty large.
A good rule of thumb is that lunar lava tubes grow to about 10 times the size of their Terran equivalents.
Another aside: in Latin, the plural of rille is rima, and lava tubes are ducta. So if I start babbling about rima and ducta, you know what I'm on about.
Anyway, back to the point: how do we go about finding intact lava tubes?
 Artemis Project: Lunar Lava Tube Dimensions http://www.asi.org/adb/m/04/02/01/02/lava-tube-size.html