You're better off on foot, in sensible shoes, exploring the narrow, winding, steep cobbled streets and magnificent views from the breaks in the high ramparts and the vast terraces at each level.
There are three official routes around Dalt Vila, though you can just wander around, get lost and surprise yourself at what you find. The tourist office in Vara de Rey gives out free guides to navigate the warren of streets and there are information plaques sprouting up from the ground all over; these give you, in multiple languages, a chance to learn and do your own guided tour at your leisure, amidst the residents hanging out their washing from their balconies.
A fantastic way to discover the hidden treasures of the old town are the guided tours by Ibiza City Tour - the experienced guides will stimulate your imagination with many anecdotes and interesting facts. https://www.ibiza-spotlight.com/ibiza/daltvila_i.htm