Hi, I’ve checked this properly.
Unfortunately, The Cave cannot currently run for someone who only owns the base game and does not own the Space Age expansion.
The reason is that The Cave uses Factorio’s official belt-stacking features, including the increased stack size used by inserters and items stacked directly on belts. These features are locked behind Factorio’s Space Age expansion feature flag. This is a restriction imposed by Factorio itself, not something I can simply bypass or fix inside the mod.
For the mod to use these stacking properties, it must declare that the expansion is required. Once that flag is enabled, Factorio checks whether the player owns Space Age before allowing the mod to load. Even adding conditional code would not solve it, because the game checks the expansion requirement before any of the mod’s Lua code is loaded.
A player who owns Space Age may still be able to play The Cave in a base-game-style setup without using the Space Age planets, but someone who has never purchased the expansion cannot load the current version of the mod.
The only way to support base-game-only players would be to remove all of the official belt-stacking functionality and redesign those parts of The Cave, or create a separate reduced base-game version without those features. That would be a major separate version of the mod, not a simple bug fix.
So unfortunately, for the current version of The Cave, owning Space Age is required.
