Finding a place to stay during Tomrrowland is non trivial. I had a friend who recommended Mechelen, since it was not too far by bus (when it did run), unfortunately by taxi, it was closer to 100E most times...
Either way, Mechelen is a nice little town with a few attractions, and the main one is the central plaza is definiely worth a visit, especially for its cathedral:
like many old cities, it's surrounded by water for protection
the music box mechanism that ran the bells, was impressive:
And of course, there was the view at the top, which was excellent: