It may look daunting from the city centre and perhaps a waste of leg strength but I highly recommend this little walk up to el Morro.
It only takes about 15 mins maximum to make it to the top. Follow Colon street and there you will find a white & yellow building which leads you to the top. There's definitely no need to take a taxi.
At the top you can appreciate the size of Arica and check out the port action. You can also see the seals on the far left of the port.