If the player went to a certain point in the facility, maybe SCP-079 or something could knock the primary lighting out, making the facility scarier and more difficult, as in scarier music, ambience, more horrid events, monsters showing up more often, etc. This'll all happen until the player goes to ...

Maybe you could play some Doom 64, Silent Hill, and Sonic.exe for some ideas if you want some creepy music...

I give a big thumbs-up on the idea. It must be implemented, but I have an idea or two to make it better. If the player goes too close to the glass, an SCP-939 instance could jump on the window & scream, like mentioned before. If the player lingers around for too long, that same SCP-939 instance shou...

The maintenance tunnels should get a whole new, scarier ambience, and should look older and maybe a bit rusty, some flickering lights, maybe take a page from Silent Hill's book. SCP-106 could do a jumpscare, such as popping down from the ceiling and start chasing the player.