1. The quarry is actually private property and you can be charged with trespassing for going into it.
2. The quarry is not totally abandoned, there is occasional work there.
(Those are the simplest to avert. Don't worry though, there are more.)
3. The quarry can be pretty hazardous in of itself, actually. Huge mounds of stone and sand and gravel, sheer cliff-faces, plenty of water to drown in, holes to fall down.
4. The quarry has ample ambush spots and hiding places for Revenants and Proxies.
(Steadily getting more difficult to avoid.)
5. It is the Revenant base of operations, there are usually at least three in the quarry at any given time, and Thage's skills notwithstanding, most humans aren't going to survive getting attacked by one. Most Conduits don't, let alone normal humans.
6. The quarry is the most dangerous of Slender Man's labyrinths. It brutally attacks the mind of anyone who spends too long in there without Slender Man's permission. It doesn't even teleport you anywhere, it just makes you think it has, you start running around walls that aren't there, turning corners that don't exist, you're already incapacitated anyway and you're probably going to encounter one of the hazards from point number three. After a while, it starts eroding your memory, then your sanity, until you're nothing left but a shell.
(Major obstacles, but still not the worst.)
7. Slender Man is finely attuned to the quarry. If you go into his quarry with the intent of stealing his secret, then you are going to have to face him. And not in his passive, observant way, I mean full-on mindfuck combat tentacle mode.
(Issue number one ^.)
So yeah, the quarry is gonna be hard. It doesn't help that Slate seems to have replaced me as the quarry's overseer. He's a lot more loyal to Slender Man than I ever was and a lot more powerful. Whenever this happens, it will have to be planned meticulously. Until then, Ava is threatening me with tasing unless I sleep, so I'd better do so.