From publisher blurb:
This is a short encounter set that is systemless and intended for mid-level PCs in any OSR-style game. The design is deliberately vague in several areas to make it easy to "tweak & toss" into your current campaign. Perfect for when the party goes "left" when you expected them to go "right", any GM/DM/Judge can easily drop this into the current campaign.
It is intended to print this file two-sided and fold in half, zine-style. This PDF download consists of three pages of content (map, encounter, and basic set-up). There are a couple of hotlinks within the file taking you to the Frugal GM blog where you can download a hi-res version of the map in you so desire.
This particular tweak & toss is little more than a setup, a map, and some highlights. The expressed scale of the map is HUGE and you might want to change it, ormaybe not. If the party does decide to follow the adventure hook it'll be up to you to decide how the adventure proceedes as there isn't even a clue inserted on which way to go. This is deliberate and a possible way to get your players into a much longer underground campaign.