I am going to the Algarve and have to connect in Lisbon - can I leave the airport?

I am a UK resident and am travelling to Faro, Algarve and it's a connecting flight stopping in Lisbon for 7 hours. It would be good if we could leave the airport for a few hours as 7 hours is a long time to wait in an airport. We're travelling with TAP Airlines. I'm not sure about the rules with the European Union, but as far as I know we can travel to anywhere thats part of it without a visa