Install the game via Steam or GOG, then download the ioRtCW files from GitHub and place them in your game folder.
Because Return to Castle Wolfenstein is still a commercially active title, the safest way to download it is through official digital storefronts. download-return-castle-wolfenstein-apun-kagames-exe
While sites like "Apun Ka Games" are common in search results, they are often flagged by users for containing or forcing users to disable antivirus software, which can be dangerous. Recommended Safe Ways to Get the Game Install the game via Steam or GOG, then
Offers a DRM-free version that is often pre-patched to run better on modern systems. Recommended Safe Ways to Get the Game Offers
Often on sale for a few dollars, the Return to Castle Wolfenstein Steam page includes the single-player campaign and is compatible with modern Windows.
Available as part of PC Game Pass or for direct purchase. Enhancing Your Experience (Modern PC Fixes)