Nha Trang is compact enough to walk along the beachfront, but the city spreads inland and to the north (towards Po Nagar) and south. Taxis and Grab (the Southeast Asian ride-hailing app) are cheap and reliable for getting to and from the sites. Motorbike taxis (xe ôm) are cheaper still but require more negotiation.
Renting a motorbike is the most practical option for day trips to Ba Ho Waterfalls, Yang Bay, or the coastal areas north and south of the city. Several rental shops cluster around the hotel areas on Trần Phú and Nguyễn Thiện Thuật. Bicycles are available for hire if you just want to cruise the promenade.
For the offshore islands, day trips by boat are organised by dozens of operators in town. The standard "4-island tour" is the most popular, covering snorkelling spots and a stop at a floating bar on the bay. You can also hire individual speedboats for island-hopping at your own pace.