Having the total height of about 830m, Burj Khalifa is the tallest building in the world. It is so tall that we can observe the sunset at the base of the building, then rush to the upper floors and watch the same sunset again for the second time on the same day.
This phenomenon can only happen if the Earth is a sphere. On a higher position, we will observe the sunset later than when we are closer to the ground.
There is a difference of about three minutes between the first sunset and the last sunset. For Islamic ritual purposes, the building is divided into three zones. In Ramadan, people in the highest floors have to break their fast about 2 minutes later than people on the lowest levels.