Awesome report! remember seeing this place on TV so much when I lived in UK.
Just a little FYI the room with the sand is an unloading station. It's for when the Officers would unload their weapons before returning them. The sand would catch an accidental discharge when unloading.
This brings back memories ofthe time I attended there to modify some software. Typically, I had forgotten to bring ID and could not recall the name of the chap I was supposed to see! The lovely lady on the front desk took pity and sorted things out..
P.S. The food in the canteen was ghastly!