Although it doesn't rise to the highest parts of town, Guanajuato's funicular is worth the ride for…read morethe efficiency of the experience and the views en route.
From below, you'll see the steep stairs beside the funicular. These are not available to climb. Rather, get yourself a one-way ticket and navigate the appropriate stairs/path to get back to the town's main street. It's impossible to get truly lost on the way down and once you get down you'll know how to get back up without the funicular if you later choose to do so (the walk up takes about 15 minutes).
At the top of the Funicular are a series of shops and then, a bit further up, the al Pipila Monument. I did no research but was told by someone knowledgeable that al Pipila is Mexico's Paul Revere. More great photos can be snapped from the place right below al Pipila.
Cheap and fun and easy to navigate, if you're in Guanajuato you should definitely try the funicular at least once.