Cairns city centre is compact and walkable. Most of what matters — the Esplanade, the aquarium, the art gallery, markets, restaurants, and the marina — is within 15 minutes on foot from the centre.
Bus: Sunbus operates the city network. Coverage is reasonable for getting to suburbs like Edge Hill and the Botanical Gardens. For day trips to Palm Cove and Port Douglas, the Trans North service runs regularly.
Taxi and rideshare: Taxis are widely available; Uber and other rideshare apps operate in Cairns. For getting between accommodation and the marina for early reef departures, this is the most practical option.
Car rental: Essential if you plan to drive north to Cape Tribulation, or west to the Atherton Tablelands under your own steam. All major rental companies operate out of the airport and several have CBD offices. Note that the road north of the Daintree River ferry is unsealed in sections — check your rental agreement for restrictions.
Cycling: The Esplanade has a good shared path. Beyond that, traffic can be heavy and there are few dedicated cycling lanes. Bikes are available for rent from several operators near the Esplanade.