About a dozen cruise lines will be in Alaska this summer. Among them are Holland America (206-281-3535), Princess (206-728-4202), Royal Viking (1-800-426-0821), and World Explorer (1-800-854-3835). Side trips to the interior can be added on to most cruises. One of the best excursions is a luxury train ride to Denali National Park, home to Mount McKinley and to a spectacular assortment of wildlife. Wherever you go, try to make time for the museums and the bookstores in every town. Reading one of the endless supply of books about Alaska and the Yukon Territory will lead you to another and then another. My favorites include: Coming into the Country , by John McPhee; The Spell of the Yukon , by Robert W. Service; Travels in Alaska , by John Muir; anything by the Canadian historian Pierre Berton; I Married the Klondike , by his mother, Laura Berton; and (for its nuts-andbolts information) Fodor’s Alaska . The three most amazing things about Alaska in the summer are: it’s not particularly cold, there are masses of wild flowers everywhere, and around June 21 the sun never really sets, allowing one to marvel at the sights long into the night. And for the sights, binoculars are a must.