Ajact: Drop some useless garbage in the hole and see if you can hear it hit the bottom.
You'd love to, but currently all your useless garbage is in your sylladex, holding up vital things like your spare ammo and the broom you intend to use to fight the raptorsprite. You've already come down a long way, so it feels like you should be able to see the bottom now. You're starting to suspect, what with the way there isn't any actual light source that could be casting any of these shadows, that the only thing keeping you from seeing the bottom is render distance.