1. Khao Yai National Park is the third largest national park in Thailand and covers an area of 2,168 square kilometers. It was established in 1962, making it the country’s first national park. The park is home to several endangered and rare species, such as the gaur, Asian elephant, and clouded leopard. It also boasts a diverse range of flora, including over 3,000 species of plants. Visitors can enjoy a variety of outdoor activities, including hiking, camping, bird-watching, and wildlife-spotting. The park has several waterfalls and scenic viewpoints, including Haew Suwat Waterfall, which was featured in the movie \"The Beach\".

2. The park office is open daily from 8:00 AM to 4:30 PM. The phone number for the park office is +66 44 312 285.

3. Admission to Khao Yai National Park is 400 baht per person for foreigners and 100 baht for Thai citizens. There are also additional fees for guided tours, camping, and vehicle entry. The park is located about 120 kilometers northeast of Bangkok and can be reached by car or public transportation. There are several tour operators and transportation companies that offer day trips and overnight packages to the park.