Thankfully the audio tour is free, because it barely works at all. The handset has to "discover" the audio locations before it will show them to you, but it's really awful at such discovery.
The Santa Maria Scala (0039 577 534571; santamariadellascala.com; £4.80) is a vast art-filled building which, until 1995, was Siena’s main hospital for 800 years.