David Baird: The fastest way is to fly to Cancún, rent a car and take the fast toll road 180 towards Mérida. You need to take the exit closest to the state line, which divides Quintana Roo from Yucatán. I remember the closest exit is a little after the state line and called Nuevo Xcan. From there you backtrack along the old Federal Highway 180 with all its speed bumps until you get to the crossroads called El Ideal. You go north on Hwy. 5 through Kantunilkin to the coastal town of Chiquilá, where you can park your car and take the ferry to Holbox. You won't need a car when you're on the island, and the parking is only $3 or $4 per day. The duration of the trip depends on the state of the road between Chiquila and El Ideal. When there are a lot of potholes it slows you down.

The cheapest way is to take a local bus from Cancún. There are only a couple per day and they are pretty slow. I think it takes about 4 hours to get to Chiquilá by bus. I once caught a ride from Valladolid to El Ideal, and from there I got on a colectivo to Kantunilkin and from there a taxi to Chiquilá. It was pretty fast and cheap, but I'm afraid that there's no advantage to doing this from Cancún.

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Ann Arbor, Mich.: What is the best place in the Yucatán where I can get excellent snorkeling right in front of my hotel by just walking right off the shore?

David Baird: You can shore dive in the Yucatán from several areas. In Puerto Morelos, there's a long, shallow reef just off the coast. It's a nationally protected park so you have to have an accredited guide and wear a life jacket, which can be annoying but I've seen lots of sea creatures in those parts. Further down the coast, I would recommend the area north of Tulum starting around Akumal and continuing down the coast to Punta Solimán and Tankah. I've done some free diving in these waters and seen many rays, some sea turtles, nursing sharks and barracudas. But perhaps the best snorkeling I've had is further south on the other side of the Sian Ka'an Biopreserve, along the Majahual peninsula, between Majahual and Xcalak. Remember, however, that having snorkeling in front of your condo or hotel means that you won't have much of a beach. Beaches don't form where reefs are prominent.

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Vienna, Va.: Do you have any suggestions on avoiding getting any intestinal illness while visiting Mexico?

David Baird: I can tell you only a few things that have worked for other people and then tell you what I do. Take all of this with a grain of salt. First let's talk about things you can do, and then we'll talk about things you can avoid.

Things you can try. A lot of people swear by the practice of building up their healthful intestinal flora before making a visit to Mexico by eating a large amount of yogurt with active cultures and/or taking acidophilus pills. The idea is that a healthy bacterial population in your gut will be better able to ward of intruding microbes. There's a certain logic to this. I'm not aware of any scientific study that supports or debunks it. Others I know will take two or more tablets of Pepto Bismol per day as a preventive measure for the duration of their stay in Mexico. This is a more aggressive tack. It's been shown to reduce the likelihood of catching an intestinal disease, but taking medicine for a prolonged period can have consequences. Others put their trust in the disinfectant properties of tequila, and will take one shot of tequila neat with lunch and dinner. I know of nothing that supports this claim, but far be it from me to burst anyone's bubble.

What to avoid. Tap water. Raw vegetables that haven't been peeled. Eateries of dubious hygiene. Any foods that have been left at room temperature, especially if they are very liquid (I am sorry to have to say that salsas are the perfect medium for growing bacteria). What about ice? I get asked this question a lot. Ice can be a source of infection for bacteria, but not for protozoa (amoeba, giardia), which don't survive freezing. It would be cruel to tell people to avoid ice on a trip to a tropical country, but, fortunately, I don't have to. It's a fairly easy question to resolve. Most restaurants and bars buy ice that has been made from purified water, and this ice is made in the same way across Mexico. The manufacturing method produces ice cubes that have the rough shape of hollow cylinders. They're easy to spot in your glass and are a sign that the ice is hygienic. Plain block ice carries no such guarantee.

The longer you stay in Mexico, the less methodical you become in following your own rules. I travel in Mexico for a good part of every year. I lived there as a kid, and I lived there as an adult. And through the years I've occasionally been sick. By now I have a certain immunity built up, but every couple of years I get "re-immunized." I hardly follow any rules, except for some common sense notions about food quality. But a traveler who is going to spend only two weeks in the country should take precautions. In addition to the advice above, I tell people not to over eat or over drink because this will tax a person's digestion. Also, you should be selective in trying the local foods—you might want to prefer tamales and enchiladas, which are well cooked, over tacos and tostadas, which come with raw vegetables and room-temperature salsa. Finally, I tell people that they must learn how to be cautious without becoming obsessed about it, because it can detract from your trip if you let it.

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