This weekend it is the yearly open monument weekend in the Netherlands. You can visit more than 4000 monuments for free.
Only on this sunday (September 11th, 2011) you can visit the Palace on Dam square for free. When you want to visit the Palace, you must first get a free entrance ticket online. The Palace on Dam square is normally not open for visitors, because the royal family still uses it. That is why it is very interesting to visit it.