The mystery of the stone sofa

Hi I'm Nick and I work as a agent at M.I.High. Right now we're doing a project about the stone sofa that has been sitting in Victoria Park, we're tying to find out what's it for. Me and the other agents went to investigate in our disguises when we got there our jolly agent Ben bought us food we went to the stone sofa and started investigating. Ben started eating and while he was eating he leant on the stone cat that was on the sofa. The sofa moved and opened a passage.

Where does this lead to?