The Schengen Nations of Europe

The 29 Schengen Nations (as of Sep 2024). They allow people forced to register (PFR),  who are US citizens, to visit:

 Austria
 Belgium
 Bulgaria (Mar 31, 2024: Borderless via Air and Sea only, not by Land or Train)
 Croatia (added in Sept 2024)
 Czech republic
 Denmark
 Estonia
 Finland
 France
 Germany
 Greece
 Hungary
 Iceland
 Italy
 Latvia
 Liechtenstein
 Lithuania
 Luxembourg
 Malta
 Netherlands
 Norway
 Poland
 Portugal
 Romania (Mar 31, 2024: Borderless via Air and Sea only, not by Land or Train)
 Slovakia
 Slovenia
 Spain
 Sweden
 Switzerland

As an agreement, Schengen was signed among the five out of ten countries of the European Union members back then, on the 14 th June 1985.  Under the Schengen agreement, travelling from one Schengen country to another is done without any passport and immigration controls or any other formalities previously required.