Trekking -- The mountainous topography around St. Catherine makes for spectacular trekking. The country is rugged, however, and it's all too easy to get lost if you set out on your own. Excellent trained local guides are available here, and it would be foolhardy not to take advantage of their services.
An easy walk from Al Karm ecolodge, Nabatean Village is the remains of a 3rd- or 4th-century village built by the ancient Nabatu people. It is a particularly striking walk from Karm because of the similarities in the stone work techniques between the old and the new. Make sure that you stop on the way by the rock leopard trap, out of use since the extermination of big cats in Egypt.
If you're lucky in Wadi Farrah, you may spot the remnants of the once considerably larger ibex herds that used to grace the peninsula. There is still a small resident population here, though hunting continues to pare down their numbers and threatens them with outright extinction. There are also a number of Byzantine buildings close by to visit.
A few kilometers to the south of the modern town, Mount St. Catherine is apparently where St. Catherine's uncorrupted remains appeared several centuries after her death. At more than 2,600m (8,500 ft.), it's actually the highest point on the peninsula and offers spectacular views of the surrounding mountains, as well as the small niche in the rock where the saint's corpse was laid by the angels.