Two of the must-sees in Dutch-land would be the Spring blooms at the Keukenhof Garden in Lisse (southwest of Amsterdam) and the Queen's Day fest in Amsterdam - which we covered all in one day.
Noted the world's largest flower garden for years, the Keukenhof Garden opens to the public from the last week of March to the middle of May (typically and weather depending). The best times to see the Dutch tulips in bloom glory are usually in the last two weeks of April. I highly recommend the Keukenhof to those who love a beautiful and serene walk in the park. The colors and variety will take your breath away!
Above left: Nederlandse' national dish - The raw herring sandwich (cold, soft, mushy...not a fan)
April 30th is the Queen's Day (or Koninginnedag) and a national holiday in the Netherlands. The Queen's birthday is celebrated and solidarity and national unity commemorated on this day. People will go out and deck themselves in 'orange craze' (as a tribute to the Dutch's House of Orange-Nassau) to participate in the day's activities like food fests, fun rides, freemarkt (flea markets) and free musical performances (planned or impromptu). The largest Koninginnedag celebration is in Amsterdam, where we spent the day soaking in the festivities and a whole lot of second-hand pot smoke (yuck!).