Only Monsters Here is a setting supplement for The Nightmares Underneath (second edition) that focuses on overland exploration in a hostile wasteland full of monsters. It is a product of the Monthly Monsters patreon.
Only Monsters Here contains:
An overland hexcrawl exploration setting, with factions, landmarks, a hex map, and new rules for travel and vehicles. There is both a dangerous wasteland AND a ruined city to explore.
Numerous random tables for generating dungeons, encounters, events, settlements, and other locations.
Playable monster types, including chaos riders, dark elves, goblins, mutants, pirates, orcs, spider people, and trolls.
A complete bestiary with over a hundred different monster stat blocks.
A conversion guide for other old school fantasy role-playing games, in case you want to use this setting with a different set of rules.
A note of caution: This is an open world, sandbox style setting and it leans heavily on random tables and wandering monster encounters. There are a lot of monsters in it, but if you are looking for already-detailed dungeon maps or adventure scenarios, this may not be the book for you.
The pdf version is available at DriveThruRPG.