A decade ago, when Spotify was two years old in the UK and had just become available in the US, Chris Johnson started a musical discovery project called TAPEFEAR. He "created a script to find new music on niche music sites, cross reference Spotify to see if it was available to stream," according to a Reddit post, and besides a bit of occasional tinkering, he largely forgot about it. In total, Johnson says the script ran for a decade amassing 42,000 songs.
You can check out TAPEFEAR here. When the random songs appear, you can select "random preview" for a sample or "play on Spotify" to add to your Spotify playlist. If you like it, you can add it to "saved" and curate your favorite niche songs.
The service reminds me of Forgotify, the website that plays Spotify songs that have never been selected by a user.