There is only one NDB (nondirectional beacon) left in The Netherlands, and that is NW at Beek, or Maastricht/Aachen Airport. This airport is also “home” of Dutch Air Traffic Control (LVNL), so I sent them an email (firstname.lastname@example.org) to ask what makes NW so special. I got a friendly reply (thank you!):
LVNL has phased out all NDBs and Locators in recent years, with the exception of the NW beacon. The reason for this is that we now use satellite navigation and these beacons are no longer needed. The navigation procedures have been adjusted accordingly. This was possible in most of the airspace above the Netherlands. Only part of the airspace and route structure in the south of the Netherlands is currently too complex to use satellite navigation. As a result, more time is needed to safely introduce the satellite navigation-based procedures in the border area with Belgium. It is expected that this will be possible sometime in the coming years. After that we can also phase out the NW beacon.
Belgium still has 11 active NDBs, with SLV-386.5 in Spa and ONL-290 in Liège close to Maastricht.