befahren
to travel on
To travel on a road, path, river, or another traffic route by vehicle or ship.
Diese Straße ist stark befahren, besonders im Berufsverkehr.
This road is heavily traveled, especially during rush hour.

to travel on / explore
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to travel on
To travel on a road, path, river, or another traffic route by vehicle or ship.
Diese Straße ist stark befahren, besonders im Berufsverkehr.
This road is heavily traveled, especially during rush hour.

'Befahren' is an inseparable verb with the prefix 'be-'. This prefix makes the verb transitive, so it always needs a direct accusative object without a preposition.
Man darf diesen Feldweg nicht mit dem Auto befahren.
You are not allowed to drive on this dirt road by car.
The past participle 'befahren' is very often used as an adjective to describe a road or path. A 'stark befahrene Straße' (heavily traveled road) is a road with a lot of traffic.
Wir wohnen an einer viel befahrenen Hauptstraße.
We live on a heavily traveled main road.
You can recognize the meaning 'erkunden' (to explore) from the context. It is used almost exclusively in connection with words like 'Höhle' (cave), 'Bergwerk' (mine), 'Stollen' (mining tunnel), or 'Grube' (pit).
Das alte Bergwerk wurde seit Jahrzehnten nicht mehr befahren.
The old mine had not been explored for decades.
In the meaning 'eine Höhle oder ein Bergwerk erkunden' (to explore a cave or mine), 'befahren' is technical language. It is used by miners, geologists, or cave explorers (speleologists).
Die Gruppe bereitete sich darauf vor, die neu entdeckte Höhle zu befahren.
The group prepared to explore the newly discovered cave.
to drive / ride
'fahren' and 'befahren' both have to do with movement on a traffic route. 'fahren' usually describes the action of a person or vehicle: someone goes by car, bus, or bicycle, or drives/rides one. 'befahren' focuses on the road, path, or river being traveled on. It often sounds more formal and frequently appears in rules or descriptions. You would more likely say 'Ich fahre zur Arbeit' (I go to work), but 'Diese Straße darf man nicht befahren' (You are not allowed to drive on this road).

Diese Brücke darf nur von Bussen und Taxis befahren werden.
This bridge may only be used by buses and taxis.
Im Winter fahre ich lieber mit der Straßenbahn ins Büro.
In winter, I prefer taking the tram to the office.