Thermae 2000 is a large hilltop spa complex above Valkenburg, built around warm mineral baths and sauna facilities. It opened in 1989 and has become one of the town's main reasons to linger after seeing the caves and castle ruins.
The appeal is simple: soak, steam, and look out over the Limburg hills. It is more of a half-day pause than a quick sightseeing stop.