THE BOSTON MUSEUM OF SCIENCE presents the film ``Grand Canyon - The Hidden Secrets'' in the Mugar Omni Theater, beginning Oct. 6. This state-of-the-art movie projection system is the world's largest, featuring a 76-foot-diameter screen with an 84-speaker sound system, and is the first of its size in New England. NEAR LIFE-SIZE DINOSAURS are stomping, hissing, and roaring - with the help of computers - at the New York State Museum in Albany (until Dec. 28) and the Buffalo Museum of Science (from Sept. to Dec. 31). Additional displays and related events are also scheduled. For more information, call (518) 474-5877 (Albany) and (716) 896-5200 (Buffalo). FOR FUN-FILLED EXERCISE, THE JAPANESE are heading for one of their 18 theme mazes. The mazes have seven-foot-high walls and a labyrinth of corridors about two miles long. The object is to go through in the shortest time. One maze drew 380,000 customers in its first year. For details, contact Japan National Tourist Organization, 630 Fifth Ave., Suite 2101, New York, NY 10111. VISITORS TO MEXICO CITY interested in a day trip to the colonial city of San Miguel de Allende should investigate El Constitutionalista, the air-conditioned ``supertrain'' that departs daily at 7:35 a.m. and returns at 4:25 p.m. Cost is about $10, including a light meal. For more information write Casa Nevada, Hospicio 35, San M. de Allende, 37700, Mexico; call (from US) 01152 987 547-3190 in Mexico City; or (212) 838-2949 in New York City.