Caltabelllotta is reached by local bus (or car) from Sciacca, which is on the South coast of Sicily west of Agrigento. Sciacca itself can easily be reached by bus from Agrigento in a morning (goes on to West of Sicily). It's a splendid bus trip up the mountain with impressive outcrops of rock, though the Rough Guide reference to 'sparkling fresh streams' seemed to be poetic license. The town itself does not seem particularly picturesque, except for its terrific setting, until the bus gets up near the top. Then it is really interesting and scenic.
Two warnings though; first, be prepared for the temperature to drop about 15 degrees as you walk over the ridge onto the other side of the mountain. I am sure it does not but it surely feels like it! It still has to be done for the very different and extensive view. Second, none of the many bars are open during the earlier afternoon and it can be thirsty work trooping up and down. Even so back on the 'home' side it is worth getting close to the top in as many bits as possible. Not only are the views outstanding but the actual juxtaposition of building and rock is worth a good look.
Someone who read one of my entries was kind enough to draw my attention to this website.
This is well worth a look.