The travel company tried to identify destinations that were off the beaten track.

The idiom 'off the beaten track' refers to places that are not commonly visited or known—remote and not frequently visited by tourists. Unfrequented means not visited often or by many people, which precisely captures this meaning. Untenanted means not occupied (typically referring to a dwelling); unattended means not looked after; untoward means unexpected and inappropriate. Therefore, unfrequented is the best synonym.