After a three day stay in Amsterdam, we would like to visit the tulip fields of keukenhof on our way to Brussels. Any suggestions on what method of transportation?
You need to provide a bit more information in order to help you better. When will you be traveling? Will you have luggage? If so, how much? Who will be traveling? Family of 6 or just 2 people?
Note that Keukenhof is a huge, carefully planned botanical garden that includes dozens and dozens of tulip beds. Some commercial tulip fields can be seen from the border fences of Keukenhof. Are you saying that you also want to walk into a commercial tulip field, which is also "a thing?" I wouldn't try to do that while traveling with luggage.
The obvious method of transport between A'dam and Brussels is by train. But there is no train station near the Keukenhof gardens. You would want to take a round-trip bus or train/bus for the Keukenhof and then a high speed train from A'dam Centraal. You would want to store your luggage either at your hotel or at the train station. Plan on thegardens taking 2-4 hours to see.
I think the easiest would be to work your way from your hotel to Centraal Station in Amsterdam. Then take a short train ride to Haarlem, and just outside the station will be buses directly to Keukenhof. After your visit, you will be able to take a bus to Schiphol Airport, where you will have a selection of trains to Brussels. Buses also leave or Keukenhof from the RAI station in Amsterdam, but it can be time consuming to get to.
The difficulty is, if you want a fast train to Brussels, you should buy the tickets well ahead for best price, but it will be hard to estimate what time you get to catch the train. If cost is not a big factor, just wait until you get to the airport to buy a ticket, if the fast train price is OK get that, otherwise you can get there by Regional/Intercity trains.
Edit: The other thought is that you will have bags I assume. If so, then heading directly to Schiphol airport, stashing the bags in a locker, then take the bus to and from Keukenhof directly might work better.
Hi, the Keukenhof offers a "combined ticket" with entrance for the Keukenhof plus bus from Leiden, Haarlem, Schiphol Airport or Amsterdam. The bus stop in Amsterdam is actually at "Europaplein", which is directly in front of the subway station with the same name on the Noord-Zuid subway/metro line 52, which is direct from Amsterdam Central Station.
You can see it all here: https://keukenhof.nl/en/ov/
So if you can store your luggage at your hotel, you could do a trip to Keukenhof from Amsterdam, taking the bus there and back, or if you don't mind paying a bit extra to store your luggage at Schiphol airport, you can take a train to Schiphol, store your luggage there, take the bus to Keukenhof and back to Schiphol, pick up your luggage, and travel onward to Brussels. This will be faster travel-wise, since Schiphol is closer to Keukenhof than Europaplein and on the way to Brussels you won't have to go back to Amsterdam.
Here is info about luggage storage at Schiphol Airport, costs 6 to 9 euros per bag: https://www.schiphol.nl/en/at-schiphol/services/luggage-storage
There are no cheap high school or museum type lockers at Schiphol.