Iphone 5s does not turn on

Hello,

I am currently in the UK traveling and I was out in the sun today. My iphone did not want to turn back on after a few minutes of heat. Although it had 70% of battery. Hours have passed by and it still does not turn on. I tried charging it to see if it will turn on but no sign light is seen. The screen continues to be completely blacked out. What should I do? Can I go to a apple store here in the UK to get it checked?