The GR 92 is one of the extensive Grande Randonnée (or GR) network of paths and trails. The trail crosses Catalonia in Spain, from the Portbou down to Ulldecona along the Mediterranean coast. With its 583km you'd better be prepared.
A note on footwear - approximately 80% of the hikers wear full hiking boots and thick socks. While running sneakers may suffice (and Choco-style sandals may work for a few days), your risk of injury is higher, and much of the trail involves hopping around on wet and/or sharp rocks. Choose conservatively, depending on the length of your hike and your experience.
Sunburn is a particular problem. Wear clothing such as long sleeve shirts and long pants as they protect from the sun, scratching branches, and insects. Bring sunscreen and a wide-brimmed hat. The track is not always well indicated, so don't forget a walking map or a G.P.S.
Related: Spain
Related: Catalonia