National monument for the Dutch Rescue Service
The answer to prize question 5 is: In Den Helder, erected in 1935 as a national monument for the Dutch Rescue Service and unveiled by Queen Wilhelmina. It has a carillon with 30 bells and is called 'Helden der Zee'.
The square where the monument stands was formerly called 'Westplein' but was later renamed 'Helden der Zeeplein'. The residents of Den Helder also refer to the monument simply as 'Het Carillon'. The monument was restored in 1999.
Thanks to Cees Janssen for this puzzle. 
It is certainly remarkable that the stamp (1933) existed before the actual monument was there (May 1935).
'@His
Sharp observation regarding the timeline of the seal and the unveiling.
Design and construction precede the inauguration by the Queen.
More background http://rijksmonumenten.wikia.com/wiki/Rijksmonumentnummer_508488
In fact, the stamp was issued to raise money for the construction of the monument!