Originally Posted by
planesquid
A few years ago, while surfing the internet late at night under the influence I happened upon a very cheap flight to Basel, which has always fascinated me due to its location on the border with France and Germany, and a week or so later I did:
CH - FR - CH (on foot)
CH - DE - CH - DE - CH (the latter 4 crossings were on a scheduled bus route)
CH - DE - CH (on foot, the only time I got stopped and questioned)
Geographically the airport counts as FR - CH - FR, but not from a border control point of view.
I'm sure someone here will have done more.
I have crossed DE-CH-LI-AT (trains) in one day and AT-LI-CH-LI-AT (bus and foot). I am sure I have crossed IT-VA-IT-VA-IT-VA-IT innumerable times in a single day, but that is a special exception. If you live near one of the exclave/enclave situations of Belgium/Netherlands, you could cross the border a dozen times in an hour, but again a special exception.