The interior spaces are likely huge, with diameters on the scale of 100's of meters, and not only do they provide a nice thermal environment, but they also provide shielding against micro-meteors and radiation.

However a lot of study is needed before placing any humans in one- clearly they are not perfectly stable, otherwise these skylights would not exist. A 10-ton slab falling on a habitat would be disastrous even if the gravity is low there. Moon-quakes do happen often- with a cycle frequency of ~27 days.

The tubes certainly can capture people's imagination, and they certainly captured mine- I personally feel they should be made a high priority for study. So I have thought about how to study them.

Like integrated electronics, the field of integrated photonics promises to be revolutionary. The ability to package lasers and complex optical devices on a chip integrated with electronics opens up the possibility of extremely compact lightweight powerful instruments. One such possibility is a LIDAR on a chip.

You can make an optical phased array where emitters and receivers are arrayed on a chip with spacing on the order of the wavelength, allowing you to transmit a directed beam from the flat surface of the chip by controlling the phase of the individual emitters- combined with detectors and processing electronics this can be engineered into a LIDAR that is EXTREMELY compact.

It could be lowered on a tether into a Lunar lava tube, or- even more exciting- FLOWN into a Mars lava tube on a drone to map the interior. Sensors for long term monitoring of lava tubes should be left in place to determine stability...

Unlike ER, I do think we should establish a presence on, and around, the moon as a stepping stone to Mars, and Lava tubes are a promising location to consider.