Travelling to Thailand through Shanghai (15 hour layover at airport). Can I go into the city?

Must I remain in the Shanghai Airport or am I allowed to travel into the city? Will I need any specific documents? And if so, then where can I obtain them and what is the approximate cost?
I am a citizen of the United Kingdom and will be travelling from Toronto, Canada to Thailand for 1 month. Then returning to Toronto. I am a Permanent Resident of Canada.