On this card it translate to "Harz Narrow Gauge Railway." Harz Narrow Gauge Railways (HSB) is a railway company that operates a 1000 mm gauge network in the Harz Mountains, in central Germany. It mostly employs 1950s vintage 2-10-2 tank locomotives, hauling traditional open platform bogie carriages. It employs 249 people. 

Bissen is a small commune and town in central Luxembourg. There are about 3500 people who live ther. It is home to a steel factory, operated by ArcelorMittal, which is the second largest steel manufacturer in the world. 

The sender was attending the First Postcard Convention in Berlin, where they were also celebrating Postcrossing's 20th anniversary. It looks like about 20 people were at this particular meetup. 

A neat vintage card, probably from the 1960s of Mammoth Hot Springs in Yellowstone National Park. Mammoth Springs is a large complex of hot springs on a hill of travertine (fresh water limestone depostied around mineral springs). It was created over thousands of years as hot water from the spring cooled and deposited calcium carbonate - over two tons flow into Mammoth each day in a solution). 

A Postcrossing meetup card from Frankfurt am Main in July of 2025. It's a 20th anniversary of Postcrossing card. It looks like about 15 people were at this meetup.

Vail Ski Resort in located near the town of Vail in Colorado. It is the third largest single mountain ski resort in the United States. It opened in 1962. Vail Ski Resort is modelled after Bavarian village styles with pedestrian streets. There are 39 ski lifts of various types - gondola, high speed six, high speed quad, fixed triple, T-bar, and platters.  I think this card must be an ad card for these guys. My first thought is they were 'finance bros." On the back, however, it reads "Christopher, Denton, Kendall, the skiing real estate brokers."