стадиону

In a sentence

• Ишао сам на велики концерт на стадиону.

  I went to a big concert at the stadium.

  The word 'стадиону' here is used in the dative singular form referring to a location 'at the stadium'.

• На стадиону је одржан важан фудбалски меч.

  At the stadium, an important football match was held.

  The word 'стадиону' is again in the dative singular form, indicating the location where the event took place.

• Деца су се играла око улаза на стадиону.

  The children were playing around the entrance at the stadium.

  Here, 'стадиону' serves the same function, specifying the vicinity of the location.