The Dutch word for outside is
buiten

Dutch Definition

buiten	©
1. adv. outside
Het is mooi weer, laten we buiten spelen. - The weather is nice, let's play outside.
2. prep. outside, out of
3. n-n. A mansion and its surrounding estate in the countryside.

buitenkant
1. n-m. the outer side: outside
De buitenkant van het gebouw is blauw geschilderd. - The outside of the building is painted blue.
aan de buitenkant - on the outside