On a warm afternoon in Aachen's old town, two American families pedaled up to me to say hello. They had been traveling in a pack, with a few kids on smaller bikes beside them and toddlers strapped into bike carts, ice cream cones melting down their small fists.
They'd taken a river cruise in the Netherlands from Rotterdam to Maastricht earlier in the week, then hopped on bikes for the ride across the border into Germany to spend an afternoon wandering Aachen's medieval streets.
Such a casual, cross-border day trip is common in Aachen, a city of roughly 260,000 people located closer to the Netherlands than to most of Germany.
After realizing its proximity to its neighbor, I learned you can bike between the two countries in as little as one afternoon. And if you're feeling really adventurous, you can add two more countries by jumping on the Vennbahn, a former railway line converted into a bike path that takes riders into Belgium and Luxembourg.
The Vennbahn's full route stretches 125 kilometers (roughly 78 miles) from Aachen to Troisvierges. That takes you across three countries—Germany, Belgium and Luxembourg.
If you want to make it four countries, start in the Netherlands. Bike from Maastricht to Aachen, where the Vennbahn begins. It adds about 34 kilometers (21 miles) to the first leg of your trip.
Riding the whole thing from Maastricht to Troisvierges takes about nine hours of riding time, according to Google Maps. Most cyclists split the ride into six stages (seven, if you count the Netherlands leg).
Once you reach Troisvierges, riders have three ways back to Aachen. They can pedal the route in reverse, hop a train, or call a taxi.
The train is the fastest option. From Troisvierges, riders can buy a ticket with a bike supplement at the station vending machine, then travel to Angleur, Belgium (about 1 hour 16 minutes), transfer, and continue on to Aachen (about 1 hour 2 minutes), for a total trip of roughly 2.5 hours.
Belgian Railways recommends avoiding peak travel times with a bike, since space is limited and bikes must load exactly where and when a crew member directs. Eurostar and ICE trains exclude bikes entirely.
For a private option, Taxi Feyen, based across the border in Amel, Belgium, will pick you up for a return trip by car and can be booked ahead by phone or email.
For travelers without a multi-day window, a shorter bicycle loop from central Aachen leads to the Dreiländereck Aachen, or Three-Country Point, where the borders of Germany, Belgium and the Netherlands converge on a hilltop called the Vaalserberg.
At roughly 1,058 feet, the Vaalserberg is the highest point in the Netherlands, and the marker there lets travelers plant one foot in each country at once.
Here's a fun trivia fact: From 1830 to 1919, this spot was a four-country point including Neutral Moresnet, a tiny independent "micro-nation" created after a dispute over a zinc mine. The territory no longer exists, as Germany annexed it in 1915 after World War I.
Two observation towers and a few hiking trails can be found at the tri-point for anyone who wants to make a full afternoon of it.
Fountains show up on nearly every block of Aachen's old town, along with the smell of sulfur-rich mineral water running underneath the city.
More than 30 thermal springs sit beneath Aachen's cobblestones, some reaching 158 degrees Fahrenheit, among the hottest in Europe. They existed long before anybody built buildings, but they were a major attraction that brought settlement to the area reaching back as far as 2,000 years ago.
In fact, the infamous Carolingian emperor Charlemagne chose Aachen as the capital of his empire specifically for its hot, sulfuric water. He built his chapel and meeting hall on a site above one of the springs, and he's buried in the cathedral that still stands in its original spot. (His throne is on the building's upper floor.)
By the 18th century, Aachen had become one of Europe's most fashionable spa towns. Its name, "Aachen," can even be derived both from the Old High German word "ahha" (water), which also, in my opinion, seems closely related to the Latin "aqua."
Today, marble plates near the historic bathhouse list Aachen's many famous visitors over the years, including Peter the Great, composer George Frideric Handel and painter Albrecht Dürer.
As I learned during my visit, Aachen's bathing tradition continues today at Carolus Thermen, a modern facility built around Aachen's Rose Spring, a source of fresh mineral thermal water.
Inside, you'll find a canaverous, column-lined bathing hall, with indoor and outdoor thermal pools kept at different temperatures. There are also saunas and relaxation rooms.
When I visited, the scene had the energy of a neighborhood pool, as opposed to a quiet, luxury spa. But that was part of the appeal, as the culture of public bathing houses goes back 2,000 years in Aachen. You could feel it. A group of teenagers roughhoused in the water, switching between fast, colloquial German and polite English apologies whenever they accidentally splashed a tourist (including me). Another man near me seemed to be napping, with his head leaning up against the side of the pool, totally unbothered by the noise.
The funniest part of visiting Carolus Thermen was that a statue of Charlemagne, rumored by historic legends to tower seven feet tall, loomed over the pool from a nearby ledge. I felt like he was always watching.
Getting there: Aachen has direct train connections to Cologne, Brussels and Maastricht, as well as most train lines within Germany. It's an easy add-on to a Rhine river cruise or western Germany itinerary.
Best for: Cyclists, history lovers and anyone who wants a taste of a local spa day with a legendary backstory.
Pack for it: Bring a swimsuit, cover-up and flip flops for the thermal baths. Also bring comfortable sneakers or cycling shoes if you're biking any stretch of the Vennbahn.
A quieter historical detour: For a poignant moment of recognition, visitors can walk past the house where Rosa Holländer, Anne Frank's grandmother, once lived before the Frank family fled to Amsterdam and see the Anne Frank historical marker. This stop adds a deeper layer to the city's history beyond its Charlemagne lore.
For a sweet stop: The tasty Aachener Printen cookie is the city's answer to gingerbread. It's worth seeking out at Nobis, a historic bakery dating back to 1858 with locations all over the city.
How this was made: AI assisted with structure, formatting, interview transcription and metadata. All reporting, product testing, research, interviews, fact-checking, writing and editing was done by Megan DeMatteo, an independent writer and editor who, like many solo creators, handles the full workload of a traditional newsroom team.
Disclosure: The author visited Aachen on a hosted press trip with the Historic Highlights of Germany. Hosting organizations do not review content before it is published. All opinions, reporting, and recommendations are entirely her own.