Over the years of staying in the Western Cape, I've managed to do quite a few amazing and beautiful hikes and trails. I thought I'd share a very short list of my favourites, and hopefully encourage you to do them if you haven't already or do them again if you have :)
In no particular order:
Devil's Peak

There are quite a few paths to go up to Devil's Peak, but my favourite has to be the most difficult one I've done to date. Amazing hike with amazing rewards and a healthy dose of danger.
Silvermine

Silvermine is hands down my favourite nature reserve. There are enough trails to never get bored there, and all of them are beautiful. There's just something about the air that side. Even if you don't do the trail linked above there are routes for running, hiking or you can even just go for a swim at the dam.
Krom Rivier

A shortish drive outside of Cape Town, this is one of the most rewarding hikes/runs I've been on. Following a river the entire time and ending up at a waterfall with a jump - who could ask for more.
Table Mountain

If you're going to include hikes in the Western Cape, you cannot exclude Table Mountain. I've done almost a dozen different routes on this mountain and there are still many more to do.
Lion's Head

Last, but not least, is probably the most accessible hike in Cape Town. Lion's Head can be an easy-ish Sunday hike, or a tough trail run.
And those are my top five trails so far :) I would love to hear about yours, so drop me a line and let me know!