Sri Lanka gained Independence from Great Britain in 1948. Since then, February 4th has been celebrated all over the country, especially in the capital. In Colombo, the President raises the national flag himself and gives a speech along with other public figures. The official ceremony is followed by a military parade where you can see tanks and aircrafts. This might also be one of the few occasions where you can witness an elephant marching with the military during a parade.
The official celebration is followed by cultural performances, music, and dances. Independence Day is a good occasion to see the culture of Sri Lanka at its best and brightest.