Khao Yai National Park is located north of Bangkok (175km, 2.5hr drive) and is the 3rd biggest national park in Thailand, with more than 2000 km² of dense forest and grassland. The park has a good website for booking of campsites and park info: https://www.khaoyainationalpark.com/en/about. The park has 7 hiking trails of which some can be done without guide, while others need a guide to be booked at the visitor centre, in the middle of the park. The park is home to a lot of wildlife, incuding elephants, hornbills, and gibbons. Some waterfalls can be visited as well. We stayed overnight at a beautiful glamping (Lala Mukha) a few kms outside the South entrance, a truly amazing place. We took a 1-day guided 4-wheel drive wildlife spotting tour booked through tontontravel. The tour guides are highly efficient in spotting animals, and are in contact with other guides to warn each other when wildlife is seen (such as elephants in our case). Another day we walked to the crossroad of the glamping road and the road to the national park, and rented a motorcycle at the gas station/car repair shop. Great way of visiting the national park, and we even drove up towards the North entrance. On the national park website, all information on where to find the viewpoints and waterfalls (when we were there it was dry ...) can be read, so no need to repeat it here, but the roads through the park are very good, and the park is beautiful.  No day-per-day description here, as we were only here for 3 days, which is sufficient to visit this national park.