It is! - except it's to hide the fly tower from the outside. The fly tower wasn't part of the original design. The first resident theatre company to be - the Royal Shakespeare company insisted upon one so the architects but came up with the genius idea of hiding it with a conservatory. I discovered this when working in the theatre space. I went exploring the fly tower (as you do) and opened a door at the top. I assumed I'd see some dark service corridor, but instead emerged into the warm, humid, nighttime air of a huge conservatory - it was easily the most magical architectural experience I've ever had.