Mention the fact that you're a senior when you make your travel reservations. By far the best way to get around in the Benelux lands is by public transportation -- metro trains, trams, and buses for short journeys, and trains for longer journeys. All three countries offer discounts for seniors on public transportation. For train travel, these discounts begin at age 65 in Belgium, and at age 60 in Holland and Luxembourg. Bus companies may have different starting ages for discounted tickets and passes. Many sightseeing attractions and tour companies offer senior discounts, but these might apply only to local residents when they produce an appropriate ID. Be sure to ask when you buy your ticket.
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.