The Keukenhof (named after the castle that is located just outside the Keukenhof grounds) is one of the major tourist attractions near Amsterdam.
It is the main flower exhibition in the Netherlands, the largest in the world, which opens every year for a few months in the spring, and attracts close to a million of visitors every year.
On the Keukenhof grounds you can see all kinds of (bulb) flowers blossoming in many colours.
Visiting the Keukenhof is a day trip from Amsterdam. The garden is quite large, and on it are various pavillions, and also a windmill (which can not be visited).
Most tour organizers will include the Keukenhof in their list of trips, but you can also venture there on your own account. You can get there by public transport (although not very easily), information about that is on the Keukenhof website.
There is free WiFi throughout the park.
Keukenhof Flower garden
Daffodil on Keukenhof