The city of Monterrey is surrounded by mountains, lots of them. They aren’t exceptionally high mountains so you won’t need to worry about elevation but they are steep. Really steep + the trails don’t exactly “switch back” so you’re often hiking straight up the mountainside.
The biggest obstacle I’ve had while attempting to explore the mountains down here is the complete lack of trail markings or obvious trailheads. But, through trail + error I’ve found a few routes up Cerro de la Silla, the iconic ridge of summits you see in a lot of Monterrey photos.