If you haven't heard of Keukenhof, it is this massive tulip garden near Amsterdam. To my dismay, I realized that the season for Keukenhof is in May! Somehow my research wasn't extensive enough and I chose to go Amsterdam in February =(
So if you ever want to go Amsterdam, please do it in May! Or late April. This is the period when the tulips are in full bloom.
If I am not wrong, it is rather expensive to go to Keukenhof, so perhaps a day pass would be better. But in general, things are not exactly cheap in Amsterdam.
Airplane tickets are easily sold out as the whole world goes to Keukenhof, so do buy early or be prepared to spend on the tickets.