This is a tangent, but all my adult life I thought that construction workers are fascinating and I wondered why the occupation is not more popular among kids. When you pass a construction site, you see the workers walking around, shouting a bit, hammering some small seemingly insignificant thing (or driving a powerful machine which is cool on its own), but over time an enormous structure rises around them, and it seems that they were just there, doing their thing and that was all it took. It fascinates me. In part because the process is counter-intuitively ungrandiose, at least if you're just a casual on-looker, but the result is grandiose and exceptionally material, as opposed to say an intellectual project's result.

I think just describing what's down there (or, more precisely -what we suspect might be down there, given our lack of knowledge!) may be sufficient.

That, and stressing that rather than committing years of your life to sitting inside a titanium cylinder being transported to wherever, you get to do real science within hours of entering an infinitely stronger titanium cylinder - and be back with your family in time for the weekend. (Yes, I exaggerate - but you get the idea. :)