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Photo: F.Eveleens, CC BY 3.0 via Wikimedia Commons
A UNESCO World Heritage Site since 2014. It is an icon of 20th century industrial architecture. It looks great even from outside. It is also well visible from the train (left side if the train goes to Rotterdam from the Hague).
The former Van Nelle Factory on the Schie in Rotterdam, is considered a prime example of the modernist and functionalist architecture. It has been a designated UNESCO World Heritage Site since 2014. Soon after it was built, prominent architects described the factory as "the most beautiful spectacle of the modern age" and "a poem in steel and glass".
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De Speelman was built in 1712. Heavily damaged during World War II, it was restored and moved to its present location.
Stichting RoMeO
Located in an old tram depot, the museum has dozens of old trams, metros and buses on display that at some point in time services the greater Rotterdam area. The museum and heritage train rides through the city centre are organised and run by volunteers, so opening hours may vary wildly.
Small amusement park, mostly aimed at parents with young children and school classes. The park houses mostly animals from mainland Europe, but also has meerkats, wallabies, coatis, and several species of small monkeys.
De Prinsenmolen dates back to 1648 and worked until 1966 to keep the adjacent polder dry. It's a house now, but the mill is still in working order. It's a nice walk alongside the Bergse Voorplas lake.
De Vier Winden was built in 1776. Until 1964 it was used to grind wheat. Although the mill is not open to visitors, it has a small shop with old fashioned mill-products.