I've heard Schlendern is close but I'm not sure it captures the essence of wandering or exploring like the french word Flâneur.
I often hear flanieren, and dictionaries know the word Flaneur (without circonflexe) in general.
The meaning of the German loanword is probably the same as the original's one (judging by my French it is), but it depends on what you mean by "concept".
In my opinion, a good verb to describe what a Flaneur does would be lustwandeln, though it's not that widely used (anymore), but there is no according noun.
Then, there is Spaziergänger, of course. This kind of person can do anything from flanieren (in a very relaxed manner) to more ambitious walking (though not really intense hiking). The verb is spazieren gehen, and the activity itself is called Spaziergang.
Der Müßiggang describes enjoying yourself, having a relaxing life without any need to recover from stress or hard work. For a long time it was something only the rich could do.
Reference: growing up in France and Germany.