You would need to drive or get a taxi. Here are some directions. Its about a 30 minute drive.

If you want to do it on the bus then unfortunetly I think your only option maybe to get the bus to San An then the bus to port des torrent

Hope that helps.

you need to get to the other side of the bay.either walk round or get a little ferry boat across.not far really.then turn left at port area.you will see a road with buses on it.get a ticket for ibiza town and get on the 1st bus #3.that will take you to town..when you get off you will see a bus station ok.you must get a another ticket from there when you come back..if you turn so your going the other way to the cars.walk down road which will lead you to the port area just turn right at bottem..walking down that road when you see kfc .you can turn right and straight up the hill to the old town area.
should only take you less than 40/5 mins if that.depends how they are getting on with the road works they are doing,,

woody, you've completely forgoten about the new bus station in san antonio which is behind the football stadium.

spottydog many thanks i forgot about that.good job your on the ball.

Do it. A cab will probably cost you around €30 or like the others say get the buses