You will see them within minutes of arriving: small three-wheeled taxis with the passenger sidecar pitched at a noticeable angle to the motorcycle. They look broken until you realise the slope of the streets and watch one climb at full throttle without spilling its passengers backwards.
A ride costs a handful of pesos and is the most efficient way to get around the centre. The drivers are usually willing to make detours to viewpoints if you ask, and a short loop up to the cathedral and back to the bay is a pleasant introduction to the city's geography.