Emphasis on surprise:
* "The once bustling marketplace was startlingly silent, a stark contrast to its usual lively chaos."
* "He had always been known for his mild temperament, so his outburst was startlingly aggressive."
Emphasis on unexpectedness:
* "Despite the overcast sky, the flowers in the garden were startlingly vibrant."
* "The solution to the problem, while simple, was startlingly effective."
Emphasis on contrast:
* "The young woman's appearance was startlingly elegant compared to the rugged, mountain scenery."
* "The old house, though dilapidated, held a startlingly beautiful garden in its backyard."
Note: "Startlingly" is a strong word, so consider using it sparingly to make it more impactful.