Green, mountainous and unspoiled, Dominica is an intriguing alternative to the more-developed Caribbean islands. Sparsely populated and 30 miles long by 15 miles wide, it is volcanic and does not have the white-sand beaches found elsewhere in the region. But that has spared it the heedless development that has marred some of its neighbors. Almost one-third of the island has been set aside as nature reserves. Instead of sandy beaches, it features impressive peaks, some 5,000 feet high; spectacular waterfalls; and dense tropical rainforests that allow more than 1,000 species of plants and 172 species of birds to flourish. Because of the challenging terrain, roads mostly follow the coast. With three national parks, 300 miles of hiking trails and world-class diving, the island offers innumerable activities and excursions.