First of all this feels and looks like it was written by an adventurer clinging to their sanity after dragging themselves out of the valley, which is excellent. The opening paragraph sells the atmosphere, and each one of the tables is filled with things that feel right at home in this cold corner of the wretched world of Mork Borg. The visuals here are on the ball, the messy sketch leans in to that idea that this was made by a unlucky survivor, but the faded notes and scribbles elevate it. It might not seem like a massive element, but these details really do add a lot.
I'm have difficulties even nitpicking when it comes to criticism. The layout can be a bit tricky to follow, but that is Mork Borg and, to be fair, I would say it isn't particularly egregious. The simple black and white colour scheme works here, though part of me wonders if it colouring the background to imitate yellowed paper. I think the only thing I would suggest would be to write the numbers for each table and/or monster names in bold, just so they're easier to pick out.
All in all Beneath the Valley is an excellent entry about my favourite local in Mork Borg (mostly because of the name). With this torn note from a diary found in a ditch, you've managed to breath (un)life into the Valley.