You can walk around a little bit, but there is no exit at the end of the Barbacanas.
In general, it's a wonderful place, 3 euro entrance, and 6 euro if you add entrance to the Colegiata. We bought the combined ticket for 6 euro - we visited both Acazaba and Colegiata.
It took us 1 hour to see everything. There is an audio guide that you can download on your phone. Must see in Antequera.
Alcazaba, Colegiata, and Arco de los Gigantes - all these places are next to each other.