The Noches de Reyes (Night of Kings) takes place the evening before, on the 5th of January each year and then the Day of Kings is celebrated by people across Spain on the 6th of January.
There will be parades (Cavalcada reial) through most of the towns on the island, with each being headed by the Three Wise Men of 'Kings': Gaspar, representing Europe, Melchor from Asia, and Baltasar from Africa. In some of the larger towns they will be followed by floats and helpers who toss sweets into the watching crowds.
Being surrounded by water, the Kings arrive in many Ibizan towns by boat. In the bakeries around this time you will no doubt find "Roscón", which is like a huge doughnut, covered in candied fruits and sugar. Traditionally there is a toy or small token baked inside and the finder is said to have good fortune... although careful that you don't choke on it!