Renting a car has become the option of choice for most people wanting to do more than lying on the beach. But beware, Crete is a large island and although the road network is well-developed and improving all the time you will not travel as fast as you would in most European countries: the island is mountainous and most roads (with the exception of the northern main road also known as the National Road) are narrow and winding.
Moving around takes more time than you might think at first and driving can be tiring because it takes a lot of concentration. Apart from the effort required to drive on unknown roads, you will also need to take extra care because of the sometimes haphazard local driving habits as well as watch for flocks of sheep and goats, and the occasional chicken, dog or donkey. More information on the local driving customs here. It's worth a read.
All in all, using public transport is not a bad alternative even though it lacks flexibility. Taxis are also quite affordable. But if you really want the flexiblity and freedom to discover this wonderful island, unless you have a lot of time, you will need to rent a car.
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