The tourist information office "Toerisme Oostende" is located at Monacoplein 2.
The opening hours are:

15/03 to 14/11: open daily from 10am to 6pm (ticket sales until 5.45pm)
15/11 to 14/03: open daily from 10am to 5.30pm (ticket sales until 5.15pm)
The office is closed on 25/12 and 1/1.