We don't even have to dig the DUMBs. The tunnels have always been there.

4 unbelievable lava tubes left behind by ancient volcanoes

https://www.lonelyplanet.com/articles/how-to-safely-and-sustainably-explore-lava-tubes-around-the-world

When it comes to mysterious, eye-catching natural wonders, it's hard to beat caves and caverns - those dark spaces glittering with geologic oddities, unusual lifeforms, and winding passages that are both curiosity-inducing and a little heart pounding. But some have an added element of excitement, capturing a frozen moment in time unchanged for thousands of years – and those are lava tubes.

Unlike most caves, which form when water dissolves softer rock over a long period of time, lava tubes are created through a far more volatile, sudden process. These special kinds of volcanic caves are created when molten lava rushes and bubbles through the earth, carving out an opening. The crust hardens as it cools and the interior lava drains away through the cracks, leaving behind a hollowed-out area.

Lava tubes are a record of the past, and they give visitors a chance to travel back millions of years. These volcanic caves are hidden all over the world, but we picked four favorites that are especially good examples of just how massive eruptions can be. So go ahead, take a walk on the wild side and go with the flow to where, yes, the floor was was lava once upon a time.

Terraforming: why the Moon is a better target than Mars

https://bigthink.com/starts-with-a-bang/terraforming-moon-mars/

No matter how advanced our civilization here on Earth becomes, there’s a sobering fact we have no choice but to reckon with: Earth’s resources are finite. That not only includes the resources we typically think of, like minerals, clean water, and breathable air, but also something even more fundamental and restrictive: land area. No matter how thoroughly we develop, there’s only a finite amount of continental land area to inhabit on our planet.

While “floating cities” on the seas and oceans may someday become a possibility, the finite surface area of planet Earth ensures that, beyond a certain point, we’ll need to leave our home planet if we want our civilization to continue to grow. Although many of us have dreamed of living on another world, we have yet to find even a hint of life on a world beyond Earth, much less a fully inhabited planet or one habitable by humans. If we want a world to be suitable for us to live on, it looks like our only option will be to transform a presently uninhabitable planet into one that humans can survive on — a process called terraforming. Despite the popular sentiment that Mars is the right world to terraform within our solar system, there may be an even better option closer to home: the Moon. Here’s the science of why.