Rotterdam-Kinderdijk Cruise on Nehalennia

On one side of the Erasmus bridge, there are different boats docked at the pier, and info for various tours. On the old cruise ship "Nehalennia", you will sail for 3 hours to the "Kinderdijk" which is a famous heritage site because of it's 19 mills. If you're on a tight budget you can make the journey in a regular boat, catch a bus, and then another boat. Another day trip to consider is going to Dordrecht, which is an interesting and monumental city. The waterbus takes you there in less than an hour.