Inside the organ's main wind chest DURING the concert. I'll post some video tonight. The little round circles on the ceiling are the bottom of the valves, the brown wood bars are linked to keys, and the gray bars running the other way (top to bottom in the picture) are the stops. When the organist presses a key, the brown tracker moves, and opens any valves that have had the gray stop bars pulled. It's a 2d mechanical computer!