This secret group is very peculiar, and I am unsure if playing the notes in any specific pattern will unlock anything else. For now I have found two rooms, but there may be more.
The first is found in the tunnel under the trade center, where a button is obscured by some foliage.
Outside
Inside
I have spammed many combinations, but have yet to find anything additional to this room
The second room was found in the Sculk cave, obscured near a lone sensor
This however requires an enderpearl to get to, or an elytra if you are a skilled flyer
This is the entrance after you get into the small opening
Which reveals
Another music room!
Similar to the bamboo colored one, each button contains a different note but this time the sounds are of a different instrument
I have yet to find anything from spamming combinations thus far
If you have seen my post under Saintes Secret Rooms , you will see a book that mentions a tomb featuring drums. Could this be related to the rooms that let you play music?
