I have this playlist that's a pretty similar vibe to hippo campus. It's mainly uk artists and bands but a lot of them are pretty underground and have pretty low monthly listeners. I think a lot of the music is really good!
Hello! My playlist "Indie, alternative and experimental rock lesser known tracks!" (playlist futures fresh songs with less than 500k streams) from debuting artists and off the radar bands. Have a nice listen!
One artist that I recently discovered, and that I would consider to be unknown to most Spotify users (as they currently have less than 700 monthly listeners), is the psychedelic/stoner rock band Nap. I've especially been enjoying listening to this track from their 2017 album, Villa: