Germany
Aachen has a thermal spa tradition stretching back to Roman times — the natural hot springs (47°C) that made it a Roman settlement also attracted Charlemagne as his imperial capital in the 9th century. Carolus Thermen, built on these same springs, is Germany's largest thermal spa complex: 10+ saunas, outdoor thermal pools, Aufguss ceremonies, and Roman-Irish bathing circuits. The water's high sulphur content gives the Aachen Thermalwasser therapeutic properties recognised since antiquity. German textile-free norm in sauna areas; swimwear in pools. Aachen sits 30 minutes from both Belgium and the Netherlands, making it a natural cross-border wellness destination.
Aachen has been a thermal city since Roman times — Carolus Thermen is built directly over the ancient spring source. The water temperature at source is 53–74°C — the hottest natural springs in Central Europe.
The flagship thermal spa complex offering Finnish, Bio, and speciality saunas alongside Roman-style thermal pools fed by geothermal spring water. Walk-ins accepted on most weekdays.
Very — on the Germany–Belgium–Netherlands tripoint. Liège (35 km), Maastricht (35 km), and Cologne (70 km) all make Carolus Thermen a viable cross-border spa day.
