There is a wide variety of animal species especially birds and beautiful flowers but also mountain villages, and crop fields including the beautiful Baan Pa Pong Piang rice field terraces which are the most beautiful in Thailand. Doi Inthanon is one of the most popular destinations in the Chiang Mai province for treks (see here the treks in Chiang Mai that i recommend). There also are 2 easy and nice trails in Doi Inthanon: Ang Ka trail and its 360 meters bridge over a marsh and Kew Mae Pan Nature Trail.
Close to the top of the peak, there are two pagodas: Phra Mahathat Napha Methanidon and Phra Mahathat Naphaphon Bhumisiri built to commemorate the 5th cycle anniversary of King Bhumibol Adulyadej and Queen Sirikit. Installed on two neighboring peaks, the two pagodas house relics of Lord Buddha.
Doi Inthanon is located 85 kilometers west of Chiang Mai. Take some sweaters when you go there, the temperatures can be cold!
It is possible to stay overnight at Doi Inthanon by camping (tent rental from 60 THB) or renting a bungalow from 1500 THB per night (online reservation on the site DNP) .
To go visit Doi Inthanon, you can also book one of the tours above.