Since you cannot play an ISO file natively on Windows, you need an emulator. The only viable option today is Xenia, the Xbox 360 emulator.

Forza Horizon 1 is notoriously hard to emulate. It pushes the GPU harder than most Xbox 360 games.

Forza Horizon (released October 2012, Xbox 360) revolutionized racing games by blending the simulation handling of the mainline Forza Motorsport series with the freedom of an open-world festival setting. Its ISO file — a complete digital copy of the game disc — remains highly sought after for preservation, emulation, and revisiting this genre-defining classic.

Physical Xbox 360 discs degrade (disc rot, scratches). An ISO allows you to create a 1:1 backup, ensuring the game survives for future playthroughs — especially important since Forza Horizon 1 was delisted from digital stores in 2016 due to music/car licensing expirations.