In addition to an increasing number of pure vegetarian and vegan restaurants in all of the main towns and cities of the Benelux, the growing popularity of eating vegetarian means that many "carnivorous" restaurants have vegetarian options on their menus -- in these cases, though, watch out for nonlegit ingredients that might be employed simply through carelessness or lack of knowledge.
Outside of restaurants, street markets and specialized "bio" markets, and the organic-products shelves in supermarkets are common places to pick up vegetarian goods. Even if you don't have the means to cook vegetables, slicing and dicing for a meal or snack of raw vegetables should not present any problems.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.