Bring a sweater and wear comfortable shoes: At the high altitude of El Teide’s summit, it can get quite chilly even when it’s toasty hot at the bottom. Trails surrounding the volcano are built out of the sharp-edged lava rocks so forget flip-flops or fancy sandals and wear decent sport shoes. I dared to wear a pair of flats and had to toss them in the garbage afterwards when they got scratched and ripped beyond repair.