If you want to fly into The Netherlands, your best bet would be flying into Amsterdam. From there, you could take a train to get to Delft. There are several trains that leave Amsterdam daily, and you shouldn't have a problem getting there. Delft is actually located about halfway between Rotterdam and The Hague. Most likely you would board a train bound for Rotterdam and change over there. There aren't as many trains leaving for Delft from Rotterdam, so try to make sure you have your tickets in advance. You still might be able to get them at the last minute, but you shouldn't bank on it. You can also take a bus from within Europe to get to Delft, but this could take a very long time, depending on where you leave from. Taking the train can be much quicker, as you don't have to deal with traffic or getting lost. The only catch is that you need to pay attention to where you are because the conductors rarely announce what town they are in. The worst thing is missing your stop and arriving in a different city. You could also drive to Delft, but this could take a while as well, depending on where you leave from.