Lightest Mexico By JOHN ABNEY MERIDA, Mexico — The people of Yucatan are proud of their beautiful city. There is an old story. A Yucatan gentleman is listening to the talk of nuclear bombs and war in another part of the county. Finally he says, "Let them blow up the world when they want. I can always go back to Merida." The city is an interesting contrast in the old and the new. There are narrow streets with ancient colonial buildings. And there are wide boulevards with elegant new homes. One of the best ways to see Merida is via the horse and carriage. You find them parked along the sides of the plazas in the center of town. A strange contrast to the new taxis but they still are popular. You can rent a carriage for the sights of Mayaland. Merida is sort of the center for tours to the ancient Maya cities. Mr. Freddy Barbachano, who owns the Panamericana among other hotels, also operates a first class travel agency in his hotel. Everything here is Barbachano and Barbachano operates nothing but top level. People come in to Merida and get themselves booked for side trips to Uxmal, Chichen Itza or Coxumel. Or half a dozen other places whose names I cannot even spell, let along pronounce. It is a handy operation for the client who merely takes time to walk in the Barbachano offices and let them know what he wants. Then spends the rest of the time riding a carriage around town. Or splashing in the hotel swimming pool.