The Netherlands is famously flat, but some parts are flatter than others. Fortunately, where I live, the landscape has a bit more character—perfect for XC mountain biking. The climbs are never brutally steep, which means you can maintain a nice rhythm of ascending and descending without burning out.
I feel lucky to be part of the trail crew at: https://www.mtb-rijkvannijmegen.nl/ and I think we maintain some of the best trails of the Netherlands.
While I love XC mountain biking and cycling in general, my heart really lies in descending and jumping. For that style of riding, we often venture to spots in Germany, Belgium, and elsewhere in Europe where the terrain is more varied. Closer to home, though, we have Bikepark Mook—the perfect place to practice jumping skills without traveling far: https://bikepark-mook.nl