The port cities on Mexico's west coast are referred to as the Mexican Riviera. There are a couple dozen cities comprising the Mexican Riviera, but I'll be focusing on the ones most visited by mainstream cruise lines.
1. In Puerto Vallarta, go ziplining through the jungles.
2. In Mazatlan, follow the blue line to Old Mazatlan. Yes, it's a blue line painted right on the road. It helps passengers keep in the safe areas. You'll even find volunteers in blue shirts helping direct tourists. You'll also find food and drink and nice views.
Or make your way to the cliff divers. But a heads up - they will expect to be tipped if you watch.
3. In Cabo San Lucas, go snorkeling. You'll see fish here that aren't present in the Caribbean.
On your way to the snorkel spot your tour guide will most likely make a swing by the Arch so you can snap some photos.
More info on what to do in Cabo San Lucas can be found HERE.
4. Manzanillo is the sailfish capital of the world.
Check out the giant statue in town.
Then wander the town. Probably the closest place to real Mexico we've been.
5. In Ensenada, head to the fish market. You'll see all kinds of fish. And if you're lucky you'll find a fisherman bringing in his catch - shark! - with a wheelbarrow.
More info on what to do in Ensenada can be found HERE.