A question I’ve kept asking myself… Why did Black Mesa as an organization decided to make some underground levels so small, and yet it did them at all? Digging underground isn’t an easy job, obviously. Remember that most of the metro/tube systems are rarely built deep underground (except Moscow, I guess); from time to time underground construction is actually made by excavating ditches, building things, and then bringing the soil back.
As we know from the history of Half-Life, Black Mesa was originally a complex for ICBMs, and it was later re-used for R&D operations (including R&D with rocket technology). In ICBM facility, one generally needs to have a place to keep rockets (in 60s, things changed, and rockets kept the propellant right inside themselves, allowing for rapid launches; if Black Mesa has been transformed into a R&D site before end of 60s, then some underground levels could be used to store propellant).
But no matter what, no ICBM/missile launch facility could require as much underground areas as BMRF had.
Which leads to a question: why would someone invest so much into so deep underground levels, to have just a few rooms?
What if there could be something else at the A level in Office Complex, that was simply hidden from the user?
This also applies to the Cafeteria level…