Shiny surfaces reflect UV adding to the overall amount of UV you experience
Shiny surfaces such as water, sand, brick, metal, glass, white walls, concrete (and even snow!) reflect UV radiation which contributes to the overall amount of UV you experience.
This means even if you are wearing a hat, and sitting in the shade which casts a dark shadow, you may still be absorbing UV radiation reflected from nearby surfaces. It is important to cover up in more than ways than one, for example by wearing sunglasses and a broad-brimmed hat, as well as seeking shade and applying an SPF30+ or higher sunscreen.
Be sun safe by combining an array of sun protection measures, and remember to be aware of surrounding surfaces which might be reflecting UV radiation.