Before the local Penitentiary was built a sample tower was built in San Martin Park (that is el torreon).
The fact is that some tours make a stop on it and it is just a stone tower, there's nothing else to see besides that! You can't go in it (it's locked with bars) and even if you can get in by climbing it it's full of dirt.
Unique Suggestions: Stay in the van and read a magazine or something
Fun Alternatives: Invite me a beer :P