Depends whether they like coast or history…it has both! The coastline is spectacular and worth walking if you can. Corfe castle is one of the best and most scenic in uk. But further north the county is full of ancient forts and amazing hills. The towns themselves aren’t much to speak of so take ferry from Poole…the coast beyond that is magic. Old Harry Rocks, Corfe, Lulworth, Durdle Door. Going further west do some fossil hunting on beaches near Lyme Regis. To East the New Forest (in Hampshire) is worth a visit

If significant walking is out of question do Corfe, drive new forest (ornamental drives), try lulworth cove, Lyme Regis . I love driving the hills and valleys of north Dorset too