You can get to Nikhef Amsterdam by public transport ("Amsterdam Science Park") or by car. There is on-site free parking available - please send your licence plate number beforehand so you can be registered for free access. On the A10, take exit 13 "Watergraafsmeer" and turn towards the city centre on S113. After about 1 km, take a right onto the Kruislaan (on your left will be the Oosterbegraafplaats cemetery), and on the Kruislaan continue straight ahead, via the underpass, and then still continue to drive in the same direction until you turn left just before the white building "SURF Amsterdam". You can park in lot P1A or P1E.
By train from Maastricht, the fastest route is to alight at Amsterdam Amstel station and then take the number 40 bus to "Muiderpoort Station". The bus stop "Amsterdam Science Park Aer" is the closest one to Nikhef, just after the underpass under the train shunting yard. Avoid the UvA FNWI building. Rather, enter the WCW Science Park on your left in the direction of bus travel, over a small bridge. Nikhef will be right in front of you.
You can find Nikhef at Science Park 105, 1098 XG Amsterdam.
Detailed directions: https://www.nikhef.nl/en/where-do-you-find-us/