Up and coming YouTubers sometimes can get frustrated with trying to upload and monetize their videos so they can earn money off of their view count. I've had this problem myself. There are many different websites that sell royalty free music and/or soundtracks that can get past the AdSense wall, so to speak. But that's not what you're looking for, right? You are looking for free downloadable background music of varied genres to go along with your video. These, surprisingly, are very easy to find! Somehow between Monday and now, I have crossed paths with a website that has been running for years, composing and posting videos, soundcloud links, and download links for all types of royalty free music. Some of these include horror based to calmly walking in the woods. Their range goes far and wide for anything you are looking for.
Another very simple, right-in-front-of-your-nose website for royalty free music is... YouTube itself! (Dun Dun Duuuun) Yes it's true, you can download music from the link below to use in contemplation videos, Let's Play videos and vlogs. Whichever type of YouTuber you are, there is a free soundtrack for you somewhere out there in the world.
Feel free to comment, ask any questions, or just let me know if this helped :)