Gaeta is small enough to explore almost entirely on foot, but the terrain is steep. The upper old town (Monte Orlando) requires serious climbing — good shoes are essential.
Local buses connect the lower town (Serapo and the seafront) with the upper old town, and run onward to Formia. The main stop is in the lower town near the port. Bus tickets are cheap and bought from tabacchi shops or drivers.
Taxis are available near the port and can be booked by phone, useful for reaching the Montagna Spaccata sanctuary or the higher parts of the promontory. There are no apps like Uber operating here.
By car, parking in the old town is extremely limited. If you have a car, use the car parks in the lower town near Serapo and walk up, or take the bus. In summer, traffic into Gaeta backs up for kilometres — leave the car in Formia and take the bus if you are visiting on a weekend in July or August.
In summer, boat tours run from the port offering views of the coastline, the sea caves, and the Montagna Spaccata from the water.