Those cruising out of San Diego should know the three ports of the Mexican Riviera most frequented by locally based cruise ships are Cabo San Lucas, Mazatlan and Puerto Vallarta. What does one do in these ports?

Besides the staples of city tours and beach trips, almost every port offers trips to interesting habitats, called “eco-tours” in the trade. They also provide adventure tours for those who enjoy some physical exertion, not a bad idea given the temptation to overeat and lounge aboard a cruise ship.

The combination adventure and ecology tour in Cabo San Lucas at the tip of the California peninsula involves kayaking to the Arches (Los Arcos), which separate the Pacific Ocean from the Sea of Cortez. From there, an island beach is used as a staging area for snorkeling.

A short distance down the Mexican mainland near Mazatlan, eco-touring is a boat ride through an estuary favored by brown pelicans, blue heron sea hawks and ospreys. Sometimes a tour of a local coconut plantation is offered.

From Puerto Vallarta, even farther south, a boat trip goes to the Marieta Islands for snorkeling, kayaking and birdwatching, or a bus tour goes to a tropical forest where the movie “Predator” was filmed.

The adventurous may take a half-day boat from Mazatlan to try and match wits and strength with sailfish and marlin, depending on the season. From Puerto Vallarta, bike rides and hikes lead into the Sierra Madre mountains. Tourists can take a dip at Volcanic Hot Water Spring or ride in all-terrain vehicles over some bumpy roads through dense foliage.

From here, travelers can go on a two-tank scuba expedition off the Marieta Islands, or swing via a system of pulleys, cables and platforms on a canopy adventure 10 to 70 feet above the jungle floor. Puerto Vallarta also has a pool for those who want to go into the water to pet or swim with dolphins.

Prefer more sedentary outings? The cruise lines have comfortable sightseeing bus and boat tours to various locales, tours of breweries and distilleries, outings to various factories, including those where adobe bricks and Mexican tiles are made and, of course, to plenty of venues for shopping, shopping and more shopping.

Cruise line tours are usually of high quality, but they have prices to match. Everybody gets a cut of the money: the local transportation companies, the attractions and, of course, the cruise line.

Two couples getting together and retaining a cab for the day probably could lower their costs and have more time to linger at an attraction, rather than getting on and off a tour bus on a predetermined schedule. This strategy could save money on a simple city tour, or trip to a local beach, or any easily reachable destination. But for the more complex tours, such as those above, nothing beats the reliability and safety of the cruise line product.

— Donald H. Harrison