Just seeing the recent discussions on visiting the Van Nelle Factory
I thought it may be useful to keep tabs on various Open House days around the world that may open up some bits of WHS that are otherwise out of bounds.London
: Usually third weekend in September (for 2015 it is the 19th & 20th). Bits of all four of Londons WHS are usually involved, which can provide something of a saving for tourists. However these are normally ones that you have to book in advance for worth keeping an eye on the website
: The weekend before London (for 2015 10th - 13th September). I don't know too much about how many WHS get involved in this one, but again the website
may reveal some details closer to the date.Brussels
: The Art Nouveau Biennial
happens in odd numbered years, over the course of weekends throughout the year, several of the Horta Houses are involved, they now seem to involve a large entrance fee €40.Netherlands
Open Monuments day seems to be in October as well, with the Van Nelle factory being open.