We Lurk Below Mod: It Lurks Below Gets a Fan Decompilation and Native Port

By Indie Kings | October 26, 2026

Updated October 26, 2026: A fan project called We Lurk Below Mod has decompiled Graybeard Games' 2022 game It Lurks Below and rebuilt it to run natively on Linux, with a native Windows build produced alongside. Its headline addition is online two player co-op that the released game did not offer in this build's setup.

Image: rails in an old rocky mine tunnel via Wikimedia Commons.

A Fan Decompilation, Not an Emulator

There is no emulator anywhere in this project, and that is the first thing to understand about it. We Lurk Below Mod is a decompilation of It Lurks Below, Graybeard Games' 2022 game, meaning contributors worked backward from the shipped program to recover its logic, then rebuilt it as native code for new platforms. The original shipped only on Windows, and the decompilation specifically targets the GOG build dated January 9, 2022, a 32 bit release. That target matters because decompilation work is always tied to one exact binary; the project transcribes what that build does rather than reinventing it. Platform wise, the port swaps out the two biggest proprietary pieces the original leaned on. Direct3D 11 rendering is replaced with OpenGL 3.3, and FMOD audio is replaced with SDL, so the whole game runs on Linux natively with nothing standing between it and the hardware. A Windows native build is produced as well, compiled with clang and lld-link rather than the MSVC quirks a 32 bit era toolchain would drag along, so even the Windows side is a modern compile instead of a repackaged copy. In only 19 commits the project covers the whole game, which sounds implausible until you remember that decompilation targets an existing binary; the game's logic already exists, and the work is recovering it.

Keeping the Port Faithful

Accuracy is the hard part of any decompilation, and this project's answer to it is the most technically interesting detail here. Around 200 functions in the binary carry values that the decompiler lost during translation, so the project marks and replays them to be sure behavior matches the original binary. The headline feature leans on that foundation, because the co-op in this mod is lockstep deterministic: both copies simulate every tick and exchange only player input over the network. That design is cheap on bandwidth, but it only holds if every machine produces identical results. To get there, the port includes its own math shims, with musl derived implementations of sin, cos, and atan2 in port/ilb_math.c, so floating point results stay identical across machines. The repository also ships check_determinism.sh, a script that replays the game tick by tick to smoke test exactly this property, giving the one invariant lockstep play depends on its own guardian. Build and feature toggles live in CMake modules named ILB_MOD_, covering a network play menu, local co-op bound to F5, changes to the start flow, and seasonal outfits and buildings. ILB_CHEATS exists in that system too, but it is off by default.

Co-op, Toggles, and Building It

For players, the practical questions are what you need and how much faith to put in a project this small. The repository contains no game data, so anyone who wants to run the port needs their own purchased copy of It Lurks Below; the project reassembles the game around the player's own files. Linux builds require 32 bit SDL2 and OpenGL libraries, a direct consequence of targeting a 32 bit original, and GitHub Actions CI produces downloadable artifacts so people can try it without assembling a toolchain themselves. The headline draw is the online two player co-op, which was not present in the released game's setup for this build. The mod runs its own lobby server, written in Rust, at welurkbelow.com on port 27960, so play does not depend on any matchmaking service from the original game, and the F5 local co-op option sits beside it under the ILB_MOD_ toggles. As for standing, the repository shows 1 star, 1 fork, and 19 commits as of October 26, 2026, and the README states no license for the project's own code. Take that licensing status as-is rather than as an open source claim, since nothing in the repo grants the permissions the term usually implies. Expectations should stay modest for the same reason: this is a very small project, even if the scope it covers, the entire game, is not.

Key Details at a Glance

FAQ

Is We Lurk Below Mod open source?
The README states no license for the project's own code, so that status should be taken as-is rather than read as an open source claim. The repository also contains no game data.

Do I need to own It Lurks Below to use it?
Yes. The repo contains no game data, so players need their own purchased copy, and the decompilation targets the GOG build dated January 9, 2022.

How does the two player co-op work?
It is online lockstep deterministic multiplayer that was not present in the released game's setup for this build. Both copies simulate every tick and exchange only player input, with a Rust lobby server at welurkbelow.com on port 27960.

Does the port also work on Windows?
Yes. A Windows native build is compiled with clang and lld-link rather than the MSVC quirks of a 32 bit era toolchain, while the Linux build runs the whole game natively.

What are the ILB_MOD_ toggles?
They are CMake modules holding build and feature options: a network play menu, local co-op bound to F5, start flow changes, and seasonal outfits and buildings. ILB_CHEATS also exists but is off by default.

How mature is this project?
The repository shows 1 star, 1 fork, and 19 commits as of October 26, 2026. Linux builds need 32 bit SDL2 and OpenGL libraries, and GitHub Actions CI produces downloadable artifacts, but expectations should stay modest at this scale.

Bottom Line

We Lurk Below Mod is the kind of release that only exists because decompilation lowers the barrier: in 19 commits a tiny project recovered an entire 2022 game and rebuilt it cross platform. The engineering choices are the credible part. Replacing Direct3D 11 with OpenGL 3.3 and FMOD with SDL, shimming sin, cos, and atan2 with musl derived versions, and shipping check_determinism.sh show the team understood that a lockstep co-op design lives or dies on identical simulation across machines. The risky part is everything around it. A lobby server on port 27960 is a single point of failure, one star and one fork mean almost no outside testing, and the README's silence on licensing leaves the project's own code in an unclear position. Treat it as a promising technical proof rather than a finished distribution channel, and keep your purchased copy close.

Sources

• GitHub README for SourceCodeDeleted/We_Lurk_below_Mod (rendering and audio replacements, layout, determinism approach, CMake toggles, build requirements), accessed 26 October 2026
• GitHub repository page for SourceCodeDeleted/We_Lurk_below_Mod (star, fork, and commit counts), accessed 26 October 2026

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