This was a really cool game! The atmosphere was very good, and it's really awesome that you did all the coding and modeling!
The only thing I noticed was that the movement was a bit sticky when navigating through the tunnels. I think it could possibly be because Unity's character controller doesn't handle movement and walls super well. I think there's a way to get the normal of the wall that the player is colliding with and subtract the projection of the player's movement vector onto that normal away from the overall movement vector. This may not help at all, but it was something I fought against a lot at one point so I thought that maybe it would be helpful. Feel free to disregard the suggestion if it's not helpful though haha
Great work!