One of the most impressive objects was this floating letter in the river Amstel,
The gently rocking letter is named "Dearest Friend..." and has been written by Dutch philosopher Baruch Spinoza (1632-1677). Spanish artist Darya von Berner made this object.
What the letter is about you can read here.
A few days later I watched the construction by daylight.
Here you have a better view of the handwriting of Spinoza.
And a few steps from his letter is a statue of Spinoza himself.