Why are there giant concrete tunnels in the desert?

(Old news, and late comment... apologies in advance) Regarding the space-LIGO you mentioned, i'd say you aren't completely wrong. Sure, space is a vacuum, but aren't we always being told that empty space isn't as empty as we like to think it is? I mean, to the layman, sure... it's empty. But technically, there's dust particles, and gases, and dare i say dark-matter (which is the opposite of "stuff" and we don't really know what it really is or if it's really even a thing), and depending on where you put your giant space-LIGO, you'd have to put it in some sort of solar-system'lagrange-point... right? Because unless it's in a place where it can be gravitationally pulled or pushed or influenced in any way by a space body, then gravitational-lensing comes into the equation, right? I'm a layman, not a fancy schmancy physics guru like you and a lot of your followers, so i just randomly pulled these thoughts together based on what I've seen on PBS, COSMOS, How the Universe Works, Big Bang Theory, Family Guy, the Simpsons, South Park, Stargate SG-1 & Stargate Atlantis, over the years. Samantha Carter, Dr. Weir & Rodney always said there's tons of stuff floating around in space, so it's not as empty as we'd like to think. Am i wrong in thinking.saying this stuff? Although a space-LIGO would be uber sensitive, I think ultimately, space is just too full of stuff to build one out there and expect it to be any more sensitive than one on earth. Too many considerations, and unless Xenu/Xemu and the Galactic Confederacy left us some pretty wicked tech laying around and we just haven't found it yet, i'm not so sure it's something we could EVER build. You'd have to build a vacuum tube, in the vacuum of space, which is why you're building it in space to begin with... to take advantage of the "natural" vacuumness of space. Oh, forget it. I'm confusing myself actually.