One of the coolest experiences in Cape Town is to hike up Lion's Head during a full moon. It's not too dangerous as there's a pathway that leads in a spiral all the way around the hill, right the way to the top. Once up there the city lights, the boats in the harbour and in the bay, and the stars of the sky look simply awesome.
If you're concerned about your safety - don't be. On warm summer evenings there are dozens of people making there way up to the top, so you don't have to be worried about being stuck alone on the top of a lonely hill. :)