What are the top attractions and must-see experiences in Grand Canyon National Park in Arizona, considering the park's diverse landscapes, outdoor activities, and scenic viewpoints? Could you provide a comprehensive guide to the most popular attractions, including iconic viewpoints, hiking trails, geological formations, and historic sites, while also highlighting lesser-known gems such as South Rim, North Rim, and Inner Canyon experiences? Additionally, what are the best times of day to visit these attractions for optimal views, minimal crowds, and the most memorable experiences?