Undertale is a paid game (usually around $9.99). Avoid "free" sites, as they often contain malware.
Best if you want a "DRM-free" version (no launcher required to play). Buy it at GOG.com . Undertale Download PC Game
Getting on your PC is quick and easy. Since it's an indie hit, it runs on almost any computer from the last decade. 🛒 Where to Buy and Download Undertale is a paid game (usually around $9