Going to the Netherlands and not seeing the colorful bloom of tulips, daffodils and hyacinths should be considered a sin. The Keukenhof Gardens is the biggest bulb-flower garden in the world. Only opened between March and May in a eight week period. There is direct buses from Leiden Train Station and Schipol Airport, but you can go to Hillegom and take a 4 km walk to the gardens. (16€ - adults and 8€ - children)