"Waar zijn jullie naartoe gefietst?"
Translation:Where did you bike to?
That's a different verb tense. "have been biking" is the present perfect progressive, which conveys a different time meaning than the present perfect "have biked." "Have been biking" means that you were biking in the past and continue to bike, possibly into the future. "Have biked" means that you biked during some unexpressed period of time within the past but are no longer biking.