How do I download a pre made level or environment to apply sound design to?

I am doing game sound design for a college project, how do I download a pre made level or environment to apply sound design to? I am mainly interested in using Fmod to sound design a level, and have less time to focus on building an environment. Hoping for a first person level to work with. Any ideas?

There are a ton of pre made levels on the market place to choose from, even some free ones. Either that of search the internet for free content.