Look south on a clear day and see the Atlas mountains across the straits in another freaking continent...!
Impressive. Also arrange a tour to "lower St.Michael's" which has an underground lake, though you have to be fit http://www.visitgibraltar.gi/see-and-do/natural-attractions/lower-st-michaels-cave-36
Hold on to your bags, do not expose any food or plastic which they might think has food in it.
Just walk up and down it, starting at Casemates and finishing at the Convent (the Governor's residence) or vice versa
Got to be done. You can take a cable car up, or have it as a mid-point stop on your Upper Rock tour. I'd recommend a walking tour if you can, as you can go at your own pace.
